Subject: 'Testing mail to news gateway'
From: [email-masked] ('What A Long Strange Trip It's Been'), Yale CS Mail/

Date: 5 Dec 1994 15:58:41 -0500

Testing mail to news gateway; please ignore...

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What_A_Long_Strange_Trip_It's_Been:_A_Hippy's_History_Of_The_60's_And_Beyond
(C) 1989 and 1994 By Lewis Sanders <[email-masked]> ISBN 0-9643083-0-4
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From [email-masked] Fri Dec  9 17:54:23 EST 1994
Article: 1114 of alt.sys.pdp8
Path: bigblue.oit.unc.edu!concert!gatech!howland.reston.ans.net!pipex!uunet!news.uiowa.edu!news
From: [email-masked] (Douglas W. Jones,201H MLH,3193350740,3193382879)
Newsgroups: sci.electronics,alt.sys.pdp8
Subject: Re: Need Orbis Floppy for PDP8
Date: 8 Dec 1994 17:00:29 GMT
Organization: University of Iowa, Iowa City, IA, USA
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Distribution: world
Message-ID: <[email-masked]>
References: <[email-masked]>
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Xref: bigblue.oit.unc.edu sci.electronics:94900 alt.sys.pdp8:1114

From  article <[email-masked]>,
by [email-masked] (MikeS1855):
> If anyone has an old Orbis Floppy with a PDP8-620 or PDP8E controller
> interface or knows where I might be able to find one, please let me know
> by e-mail. I am looking for one. Thank you, Mike

The above note should have been posted to alt.sys.pdp8, the preferred
newsgroup for discussion of PDP-8 systems.  The group comp.sys.dec
might also have been appropriate.

					Doug Jones
					[email-masked]

Article 1115 of alt.sys.pdp8:
Path: bigblue.oit.unc.edu!concert!theo!news-server.ncren.net!taco.cc.ncsu.edu!gatech!swrinde!pipex!uunet!news.uiowa.edu!news
From: [email-masked] (Douglas W. Jones)
Newsgroups: alt.sys.pdp8,alt.answers,news.answers
Subject: PDP-8 Frequently Asked Questions (posted every other month)
Followup-To: alt.sys.pdp8
Date: 8 Dec 1994 08:08:08 GMT
Organization: Computer Science, University of Iowa, Iowa City, Iowa, USA
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Summary: Answers to common questions about antique DEC PDP-8 computers.
	Those posting to alt.sys.pdp8 should read this.
Keywords: FAQ DEC PDP 8
Xref: bigblue.oit.unc.edu alt.sys.pdp8:1115 alt.answers:5908 news.answers:32284

Archive-name: dec-faq/pdp8
Last-modified: Dec 8, 1994

Frequently Asked Questions about the DEC PDP-8 computer.

	By Douglas Jones, [email-masked]
	(with help from many folks)

The most recent version of this file is available by anonymous FTP from:

	ftp://rtfm.mit.edu/pub/usenet/alt.sys.pdp8
	ftp://ftp.uu.net/usenet/news.answers/dec-faq
	ftp://src.doc.ic.ac.uk:/pub/usenet/news.answers/alt.sys.pdp8
	ftp://sunsite.unc.edu/pub/academic/computer-science/history/pdp-8/docs

Automatic translations of this document to HTML format (as used by World Wide
Web) are available from:

	http://www.cis.ohio-state.edu/hypertext/faq/usenet/dec-faq/top.html

An obsolete version of this file is available on the Walnut Creek USENET
FAQ CDROM.

This posting conforms to RFC1153 USENET digest format (with exceptions due
to the fact that it is not really a digest).

Contents:

	What is a PDP?
	What is a PDP-8?
	What is the PDP-8 instruction set?
	What does PDP-8 assembly language look like?
	What character sets does the PDP-8 support?
	What different PDP-8 models were made?
	What about the LINC-8 and PDP-12?
	Where can I get a PDP-8 today?
	Where can I get PDP-8 documentation?
	What operating systems were written for the PDP-8?
	What programming languages were supported on the PDP-8?
	Where can I get PDP-8 software?
	Where can I get additional information?
	What use is a PDP-8 today?
	Who's Who?

----------------------------------------------------------------------

Subject: What is a PDP?

In 1957, Ken Olson and Harlan Anderson founded Digital Equipment
Corporation (DEC), capitalized at $100,000, and 70% owned by American
Research and Development Corporation.  The founders wanted to call the
company Digital Computer Corporation, but the venture capitalists
insisted that they avoid the term Computer and hold off on building
computers.  With facilities in an old woolen mill in Maynard
Massachusetts, DEC's first product was a line of transistorized digital
"systems modules", plug-in circuit boards with a few logic gates per
board.  Starting in 1960, DEC finally began to sell computers (the
formal acceptance of the first PDP-1 by BBN is reported in Computers
and Automation, April 1961, page 8B).  Soon after this, there were
enough users that DECUS, the Digital Equipment Computer User's Society
was founded.

DEC's first computer, the PDP-1, sold for only $120,000 at a time when
other computers sold for over $1,000,000.  (A good photo of a PDP-1 is
printed in Computers and Automation, Dec. 1961, page 27).  DEC quoted
prices as low as $85,000 for minimal models.  The venture capitalist's
insistance on avoiding the term computer was based on the stereotype
that computers were big and expensive, needing a computer center and a
large staff; by using the term Programmable Data Processor, or PDP, DEC
avoided this stereotype.  For over a decade, all digital computers sold
by DEC were called PDPs.  (In early DEC documentation, the plural form
"PDPs" is used as a generic term for all DEC computers.)

In the early 1960's, DEC was the only manufacturer of large computers
without a leasing plan.  IBM, Burroughs, CDC and other computer
manufacturers leased most of their machines, and many machines were
never offered for outright sale.  DEC's cash sales approach led to the
growth of third party computer leasing companies such as DELOS, a
spinoff of BB&N.

DEC built a number of different computers under the PDP label, with a
huge range of price and performance.  The largest of these are fully
worthy of large computer centers with big support staffs.  Some early
DEC computers were not really built by DEC.  With the PDP-3 and LINC,
for example, customers built the machines using DEC parts and
facilities.  Here is the list of PDP computers:

    MODEL  DATE  PRICE     BITS  COMMENTS
    =====  ====  ========  ====  =====
    PDP-1  1960  $120,000  18    DEC's first computer
    PDP-2            NA    24    Never built?
    PDP-3            NA    36    One built by a customer, not by DEC.
    PDP-4  1962   $60,000  18    Predecessor of the PDP-7.
    PDP-5  1963   $27,000  12    The ancestor of the PDP-8.
    PDP-6  1964  $300,000  36    A big computer; 23 built, most for MIT.
    PDP-7  1965   $72,000  18    Widely used for real-time control.
    PDP-8  1965   $18,500  12    The smallest and least expensive PDP.
    PDP-9  1966   $35,000  18    An upgrade of the PDP-7.
    PDP-10 1967  $110,000  36    A PDP-6 followup, great for timesharing.
    PDP-11 1970   $10,800  16    DEC's first and only 16 bit computer.
    PDP-12 1969   $27,900  12    A PDP-8 relative.
    PDP-13           NA          Bad luck, there was no such machine.
    PDP-14                       A ROM-based programmable controller.
    PDP-15 1970   $16,500  18    A TTL upgrade of the PDP-9.
    PDP-16 1972      NA    8/16  A register-transfer module system.

Corrections and additions to this list are welcome!  The prices given
are for minimal systems in the year the machine was first introduced.
The bits column indicates the word size.  Note that the DEC PDP-10
became the DECSYSTEM-20 as a result of marketing considerations, and
DEC's VAX series of machines began as the Virtual Address eXtension of
the never-produced PDP-11/78.

It is worth mentioning that it is generally accepted that the Data
General Nova (see photo, Computers and Automation, Nov. 1968, page 48)
was originally developed as the PDP-X, a 16-bit multi-register version
of the PDP-8.  A prototype PDP-X was built at DEC before the design was
rejected.  This and a competing 16-bit design were apparently submitted
to Harold McFarland at Carnegie-Mellon University for evaluation;
McFarland (and perhaps Gordon Bell, who was at C-MU at the time)
evaluated the competing designs and rejected both in favor of what we
know as the PDP-11.  Some speculate that Bell rejected the Nova design
because the competing proposal used the register-transfer notation he
had introduced in "Bell and Newell, Computer Structures -- Readings and
Examples".  An alternate story is that the reason DEC never produced a
PDP-13 was because the number 13 had been assigned to what became the
Nova; this is unlikely because the PDP-X prototype came before the -11.
Neither DEC nor Data General talk much about this, but Ed De Castro,
the founding president of Data General, was part of the PDP-8 design
team, as were many of the others who came to Data General to build the
Nova.

Today, all of the PDP machines are in DEC's corporate past, with the
exception of the PDP-11 family, which survives as a line of
microcomputers.

Of course, occasionally, some lab builds a machine out of DEC hardware
and calls it a PDP with a new number.  For example, the Australian
Atomic Energy Commission once upgraded a PDP-7 by adding a PDP-15 on
the side; they called the result a PDP-22.

------------------------------

Subject: What is a PDP-8?

The PDP-8 family of minicomputers were built by Digital Equipment
Corporation between 1965 and 1990, although it is worth noting that the
term minicomputer first came into prominence after the machine was
introduced.  The first use of the term appears to have been made by
the head of DEC's operations in England, John Leng.  He sent back a
sales report that started: "Here is the latest minicomputer activity
in the land of miniskirts as I drive around in my [Austin] Mini Minor."
The term quickly became part of DEC's internal jargon and spread from
there; the first computer explicitly sold as a minicomputer, though,
was made by by Interdata (See the Interdata ad in Computers and
Automation, May 1968, page 10).

The PDP-8 was largely upward compatible with the PDP-5, a machine that
was unveiled on August 11, 1963 at WESCON, and the inspiration for that
machine came from two earlier machines, the LINC and the CDC 160.  All
of these machines were characterized by a 12 bit word with little or no
hardware byte structure, typically 4K words of memory, and simple but
powerful instruction sets.

Although some people consider the CDC 160 the first minicomputer, the
PDP-8 was the definitive minicomputer.  By late 1973, the PDP-8 family
was the best selling computer in the world, and it is likely that it was
only displaced from this honor by the Apple II (which was displaced by
the IBM PC).  Most models of the PDP-8 set new records as the least
expensive computer on the market at the time of their introduction.
The PDP-8 has been described as the model-T of the computer industry
because it was the first computer to be mass produced at a cost that
just about anyone could afford.

C. Gordon Bell has said that the basic idea of the PDP-8 was not really
original with him.  He gives credit to Seymour Cray (of CDC and later
Cray) for the idea of a single-accumulator 12 bit minicomputer.  Cray's
CDC 160 family (see CACM, march 1961, photo on page 244, text on page
246) was such a machine, and in addition to the hundreds of CDC 160
systems sold as stand-alone machines, a derivative 12 bit architecture
was used for the I/O processors on Cray's first great supercomputer,
the CDC 6600.

Note that Cray's 12 bit machines had 6 basic addressing modes with
variable length instruction words and other features that were far from
the simple elegance of the PDP-8.  Despite its many modes, the CDC
architecture lacked the notion of current page addressing, and the
result is that, for examples that don't involve indexing, PDP-8 code is
generally as tight as and perhaps tighter than CDC 160 code.

------------------------------

Subject: What is the PDP-8 instruction set?

The PDP-8 word size is 12 bits, and the basic memory is 4K words.  The
minimal CPU contained the following registers:

	PC - the program counter, 12 bits.
	AC - the accumulator, 12 bits.
	L  - the link, 1 bit, commonly prefixed to AC as <L,AC>.

It is worth noting that many operations such as procedure linkage and
indexing, which are usually thought of as involving registers, are done
with memory on the PDP-8 family.

Instruction words are organized as follows:
	 _ _ _ _ _ _ _ _ _ _ _ _
	|_|_|_|_|_|_|_|_|_|_|_|_|
	|     | | |             |
	|  op |i|z|    addr     |

	op   - the opcode.
	i    - the indirect bit (0 = direct, 1 = indirect).
	z    - the page bit (0 = page zero, 1 = current page).
	addr - the word in page.

The top 5 bits of the 12 bit program counter give the current page, and
memory addressing is also complicated by the fact that absolute memory
locations 8 through 15 are incremented prior to use when used as indirect
addresses.  These locations are called auto-index registers (despite the
fact that they are in memory); they allow the formulation of very tightly
coded array operations.

The basic instructions are:

	000 - AND - and operand with AC.
	001 - TAD - add operand to <L,AC> (a 13 bit value).
	010 - ISZ - increment operand and skip if result is zero.
	011 - DCA - deposit AC in memory and clear AC.
	100 - JMS - jump to subroutine.
	101 - JMP - jump.
	110 - IOT - input/output transfer.
	111 - OPR - microcoded operations.

The ISZ and other skip instructions conditionally skip the next
instruction in sequence.  The ISZ is commonly used to increment a loop
counter and skip if done, and it is also used as an general increment
instruction, either followed by a no-op or in contexts where it is known
that the result will never be zero.

The JMS instruction stores the return address in relative word zero of
the subroutine, with execution starting with relative word one.
Subroutine return is done with an indirect JMP through the return
address.  Subroutines commonly increment their return addresses to index
through inline parameter lists or to perform conditional skips over
instructions following the call.

The IOT instruction has the following form:
	 _ _ _ _ _ _ _ _ _ _ _ _
	|1|1|0|_|_|_|_|_|_|_|_|_|
	|     |           |     |
	|     |   device  | op  |

The IOT instruction specifies one of up to 8 operations on one of 64
devices.  Typically (but not universally), each bit of the op field
evokes an operation, and these can be microcoded in right to left
order.  Prior to the PDP-8/E, there were severe restrictions on the
interpretation of the op field that resulted from the fact that the
operation was delivered as a sequence of IOP pulses, each on a separate
line of the I/O bus.  Each line was typically used to evoke a different
device function, so essentially, the operation 000 was always a no-op
because it evoked no functions, and the code 111 evoked all three
functions in series.

As an example of the use of IOT instructions, consider the console
terminal interface.  On early PDP-8 systems, this was always assumed to
be an ASR 33 teletype, complete with low-speed paper tape reader and
punch.  It was addressed as devices 03 (the keyboard/reader) and 04
(the teleprinter/punch):
	 _ _ _ _ _ _ _ _ _ _ _ _
	|1|1|0|_|_|_|_|_|_|_|_|_|
	      |0 0 0 0 1 1|0 0 1  - KSF - keyboard skip if flag
	      |0 0 0 0 1 1|0 1 0  - KCC - keyboard clear flag
	      |0 0 0 0 1 1|1 0 0  - KRS - keyboard read static

The keyboard flag is set by the arrival of a character.  The KCC
instruction clears both the flag and the accumulator.  KRS ors the 8 bit
input data with the low order 8 bits of AC.  The commonly used KRB
instruction is the or of KCC and KRS.  To await one byte of input, use
KSF to poll the flag, then read the byte with KRB.
	 _ _ _ _ _ _ _ _ _ _ _ _
	|1|1|0|_|_|_|_|_|_|_|_|_|
	      |0 0 0 1 0 0|0 0 1  - TSF - teleprinter skip if flag
	      |0 0 0 1 0 0|0 1 0  - TCF - teleprinter clear flag
	      |0 0 0 1 0 0|1 0 0  - TPC - teleprinter print static

The teleprinter flag is set by the completion of the TPC operation (as
a result, on startup, many applications output a null in order to get
things going).  TCF clears the flag, and TPC outputs the low order 8
bits of the accumulator.  The commonly used TLS instruction is the or
of TCF and TPC.  To output a character, first use TSF to poll the flag,
then write the character with TLS.

IOT instructions may be used to initiate data break transfers from block
devices such as disk or tape.  The term "data break" was, for years,
DEC's preferred term for cycle-stealing direct-memory-access data
transfers.

Some CPU functions are accessed only by IOT instructions.  For example,
interrupt enable and disable are IOT instructions:
	 _ _ _ _ _ _ _ _ _ _ _ _
	|1|1|0|_|_|_|_|_|_|_|_|_|
	      |0 0 0 0 0 0|0 0 1  - ION - interrupts turn on
	      |0 0 0 0 0 0|0 1 0  - IOF - interrupts turn off

An interrupt is requested when any device raised its flag.  The console
master clear switch resets all flags and disables interrupts.  In
effect, an interrupt is a JMS instruction to location zero, with the
side effect of disabling interrupts.  The interrupt service routine
is expected to test the device flags and perform the operations needed
to reset them, and then return using ION immediately before the indirect
return JMP.  The effect of ION is delayed so that interrupts are not
enabled until after the JMP.

The instructions controlling the optional memory management unit are
also IOT instructions.  This unit allows the program to address up to
32K of main memory by adding a 3 bit extension to the memory address.
Two extensions are available, one for instruction fetch and direct
addressing, the other for indirect addressing.

A wide variety of operations are available through the OPR microcoded
instructions:
         _ _ _ _ _ _ _ _ _ _ _ _
Group 1 |1|1|1|0|_|_|_|_|_|_|_|_|
	         1                - CLA - clear AC
	           1              - CLL - clear the L bit
                     1            - CMA - ones complement AC
                       1          - CML - complement L bit
                               1  - IAC - increment <L,AC>
                         1 0 0    - RAR - rotate <L,AC> right
                         0 1 0    - RAL - rotate <L,AC> left
	                 1 0 1    - RTR - rotate <L,AC> right twice
	                 0 1 1    - RTL - rotate <L,AC> left twice

In general, the above operations can be combined by oring the bit
patterns for the desired operations into a single instruction.  If none
of the bits are set, the result is the NOP instruction.  When these
operations are combined, they operate top to bottom in the order shown
above.  The exception to this is that IAC cannot be combined with the
rotate operations on some models, and attempts to combine rotate
operations have different effects from one model to another (for example,
on the PDP-8/E, the rotate code 001 means swap 6 bit bytes in the
accumulator, while previous models took this to mean something like
"shift neither left nor right 2 bits").
         _ _ _ _ _ _ _ _ _ _ _ _
Group 2 |1|1|1|1|_|_|_|_|_|_|_|0|
                   1     0        - SMA - skip on AC < 0  \
                     1   0        - SZA - skip on AC = 0   > or group
                       1 0        - SNL - skip on L /= 0  /
                   0 0 0 1        - SKP - skip unconditionally
                   1     1        - SPA - skip on AC >= 0 \
                     1   1        - SNA - skip on AC /= 0  > and group
                       1 1        - SZL - skip on L = 0   /
                 1                - CLA - clear AC
                           1      - OSR - or switches with AC
                             1    - HLT - halt

The above operations may be combined by oring them together, except that
there are two distinct incompatible groups of skip instructions.  When
combined, SMA, SZA and SNL, skip if one or the other of the indicated
conditions are true (logical or), while SPA, SNA and SZL skip if all of
the indicated conditions are true (logical and).  When combined, these
operate top to bottom in the order shown; thus, the accumulator may be
tested and then cleared.  Setting the halt bit in a skip instruction is
a crude but useful way to set a breakpoint for front-panel debugging.
If none of the bits are set, the result is an alternative form of no-op.

A third group of operate microinstructions (with a 1 in the least
significant bit) deals with the optional extended arithmetic element to
allow such things as hardware multiply and divide, 24 bit shift
operations, and normalize.  These operations involve an additional data
register, MQ or multiplier quotient, and a small step count register.
On the PDP-8/E and successors, MQ and the instructions for loading and
storing it were always present, even when the EAE was absent, and the
EAE was extended to provide a useful variety of 24 bit arithmetic
operations.

------------------------------

Subject: What does PDP-8 assembly language look like?

There are many different assemblers for the PDP-8, but most use a
compatible basic syntax; here is an example:

	START,	CLA CLL		/ Clear everything
		TAD	X	/ Load X
		AND I	Y	/ And with the value pointed to by Y
		DCA	X	/ Store in X
		HLT		/ Halt

	X,	1 		/ A variable
	Y,	7 		/ A pointer

Note that labels are terminated by a comma, and comments are separated
from the code by a slash.  There are no fixed fields or column
restrictions.  The "CLA CLL" instruction on the first line is an example
of the microcoding of two of the Group 1 operate instructions.  CLA
alone has the code 7200 (octal), while CLL has the code 7100; combining
these as "CLA CLL" produces 7300.  As a general rule, except when memory
reference instructions are involved, the assembler simply ors together
the values of all blank separated fields between the label and comment.
	
Indirection is indicated by the special symbol I in the operand field,
as in the third line of the example.  The typical PDP-8 assembler has no
explicit notation to distinguish between page zero and current page
addresses.  Instead, the assembler is expected to note the page holding
the operand and automatically generate the appropriate mode.  If the
operand is neither in the current page nor page zero, some assemblers
will raise an error, others will automatically generate an indirect
pointer to the off-page operand; this should be avoided because it only
works for directly addressed off-page operands, and only when the memory
management unit is not being used to address a data field other than the
current instruction field.

Note, in the final two lines of the example, that there is no "define
constant" pseudo-operation.  Instead, where a constant is to be
assembled into memory, the constant takes the place of the op-code field.

The PDP-8 has no immediate addressing mode, but most assemblers provide
a notation to allow the programmer to ignore this lack:

		TAD	(3)	/ add 3, from memory on the current page.
		TAD	[5]	/ add 5, from memory on page zero.
		JMP I	(LAB)	/ jump indirect through the address of LAB.

Assemblers that support this automatically fill the end of each page
with constants defined in this way that have been accumulated during the
assembly of that page.  Note that the variants "(3" and "[5" (with no
closing parentheses) are usually allowed but the use of this sloppy form
is discouraged.  Furthermore, the widely used PAL8 assembler interprets
the unlikely operand "(3)+1" as being the same as "(3+1)".

Arithmetic is allowed in operand fields and constant definitions, with
expressions evaluated in strict left-to-right order, as:

		TAD	X+1	/ add the contents of the location after X.
		TAD	(X-1)	/ add the address of the location before X.

Other operators allowed include and (&), or (!), multiply (^) and divide
(%), as well as a unary sign (+ or -).  Unfortunately, one of the most
widely used assemblers, PAL8, has trouble when unary operators are mixed
with multiplication or division.
	
Generally, only the first 6 characters of identifiers are significant
and numeric constants are evaluated in octal.

Other assembly language features are illustrated below:

	/ Comments may stand on lines by themselves
				/ Blank lines are allowed

		*200		/ Set the assembly origin to 200 (octal)

	NL0002=	CLA CLL CML RTL	/ Define new opcode NL0002.

		NL0002		/ Use new opcode (load 0002 in AC)
		JMP	.-1	/ Jump to the previous instruction

	X1=	10		/ Define X1 (an auto-index register address)
	LETA=	"A		/ Define LETA as 000011000001 (ASCII A)

		TAD I	X1	/ Use autoindex register 1

		IAC; RAL	/ Multiple instructions on one line

		$		/ End of assembly

The assembly file ends with a line containing a $ (dollar sign) not in
a comment field.

The $, * and =  syntax used by most PDP-8 assemblers replaces functions
performed by pseudo-operations on many other assemblers.  In addition,
PAL8, the most widely used PDP-8 assembler supports the following
pseudo-operations:

		DECIMAL		/ Interpret numeric constants in base 10
		OCTAL		/ Interpret numeric constants in base 8
		EJECT		/ Force a page eject in the listing
		XLIST		/ Toggle listing
		XLIST	N	/ Turn on listing if N=0, off if N=1
		PAGE 	 	/ Advance location counter to next page
		PAGE 	N	/ Set location counter start of page N
		FIELD	N	/ Assemble into extended memory field N
		TEXT	"STR"	/ Pack STR into consecutive 6 bit bytes
		ZBLOCK	N	/ Allocate N words, initialized to zero
		IFDEF	S <C>	/ Assemble C if symbol S is defined
		IFNDEF	S <C>	/ Assemble C if symbol S is not defined
		IFZERO	E <C>	/ Assemble C if expression E is zero
		IFNZRO	E <C>	/ Assemble C if expression E is not zero
		FIXMRI  OP= VAL	/ Define OP as memory reference instruction

Conditonally assembled code must be enclosed in angle brackets.  The
enclosed code may extend over multiple lines and, because different
assemblers treat comments within conditionals differently, the closing
bracket should not be in a comment and any brackets in comments should
be balanced.

------------------------------

Subject: What character sets does the PDP-8 support?

From the beginning, PDP-8 software has generally assumed that textual
I/O would be in 7 bit ASCII.  Most early PDP-8 systems used teletypes
as console terminals; as sold by DEC, these were configured for mark
parity, so most older software assumes 7 bit ASCII, upper case only,
with the 8th bit set to 1.  On output, lines are generally terminated
with both CR and LF; on input, CR is typically (but not always) the
line terminator and LF is typically ignored.  In addition, the tab
character (HT) is generally allowed, but software support output of text
containing tabs varies.

One difficulty with much PDP-8 software is that it bypasses the device
handlers provided by the operating system and goes directly to the
device.  This results in very irregular device support, so that, for
example, control-S and control-Q work to start and stop output under
OS/8, but the OS/8 PAL assembler ignores them when reporting errors.

Most of the better engineered PDP-8 software tends to fold upper and
lower case on input, and it ignores the setting of the 8th bit.  Older
PDP-8 software will generally fail when presented with lower case
textual input (this includes essentially all OS/8 products prior to
OS/278 V1).

Internally, PDP-8 programmers are free to use other character sets, but
the "X notation provided by the assembler encourages use of 7 bit ASCII
with the 8th bit set to 1, and the TEXT pseudo-operation encourages the
6 bit character set called "stripped ASCII".  To map from upper-case-only
ASCII to stripped ASCII, each 8 bit character is anded with octal 77 and
then packed 2 characters per word, left to right.  Many programs use a
semi-standard scheme for packing mixed upper and lower case into 6 bit
TEXT form; this uses ^ to flip from upper to lower case or lower to
upper case, % to encode CR-LF pairs, and @ (octal 00) to mark end of
string.  Note that this scheme makes no provision for encoding the %,
^ and @ characters, nor does it allow control characters other than the
CR-LF pair.

The P?S/8 operating system supports a similar 6 bit text file format,
where upper and lower case are folded together, tabs are stored as _
(underline), end-of-line is represented by 00, padded with any
nonzero filler to a word boundary, and end of file is 0000.

Files under the widely used OS/8 system consist of sequences of 256 word
blocks.  When used for text, each block holds 384 bytes, packed 3 bytes
per pair of words as follows:

		aaaaaaaa		ccccaaaaaaaa
		bbbbbbbb		CCCCbbbbbbbb
		ccccCCCC

Control Z is used as an end of file marker.  Because most of the PDP-8
system software was originally developed for paper tape, binary object
code is typically stored in paper-tape image form using the above packing
scheme.

------------------------------

Subject: What different PDP-8 models were made?

The total sales figure for the PDP-8 family is estimated at over 300,000
machines.  Over 7000 of these were sold prior to 1970.  During the PDP-8
production run, a number of models were made, as listed in the following
table.  Of these, the PDP-8/E is generally considered to be the
definitive machine.  If the PDP-8 is considered to be the Model T of the
computer industry, perhaps the PDP-8/E should be considered to be the
industry's Model A.

    MODEL	DATES	SALES   COST	TECHNOLOGY	REMARKS

    PDP-5	63-67	 116		Transistor
    PDP-8	65-69 	1450	$18,500	Transistor
    LINC-8	66-69	 142	$38,500	Transistor
    PDP-8/S	66-70	1024	$10,000	Transistor	Very slow
    PDP-8/I	68-71 	3698	$12,800	TTL
    PDP-8/L	68-71 	3902	 $8,500	TTL		Scaled down 8/I
    PDP-12	69-73?	3500?	$27,900	TTL		Followup to LINC-8
    PDP-8/E	70-78	>10K?	 $7,390	TTL MSI	Omnibus
    PDP-8/F	72-78?	>10K?	<$7K	TTL MSI Omnibus	Based on 8/E CPU
    PDP-8/M	72-78?	>10K?	<$7K	TTL MSI Omnibus	OEM version of 8/F
    PDP-8/A	75-84?	>10K?	 $1,317	TTL LSI Omnibus	New CPU or 8/E CPU
    VT78	78-80		<$10K	Intersil 6100	Workstation
    DECmate I	80-84			Harris 6120	Workstation
    DECmate II	82-86		 $1,435	Harris 6120	Workstation
    DECmate III	84-90		 $2,695	Harris 6120	Workstation
    DECmate III+85-90			Harris 6120	Workstation

Additional information is available in part two of this FAQ, where all
known models of the PDP-8, along with variants, alternate marketing
names, and other peculiarities are given.

The last years of the PDP-8 family were dominated by the PDP-8 compatible
microprocessor based VT78 and DECmate workstations.  DEC also used the
Harris 6120 microprocessors in many peripheral controllers for the
PDP-11 and PDP-15.  While all of the earlier PDP-8 systems were open
architecture systems, the DECmates had closed architectures with an
integrated console terminals and limited peripheral options.

The following PDP-8 compatible or semi-compatible machines were made and
sold by others; very little is known about many of these:

	MODEL		DATE	MAKER, NOTES

	MP-12		6?	Fabritek (a surviving example runs FOCAL).
	TPA		68?	Hungarian, a PDP-8/L clone, ran FOKAL
	Electrotechnica-100I ?	Yugoslavian, a PDP-8/I clone or OEM label.
	Saratov-2	?	Russian, a slow clone, perhaps PDP-8/S
	Voronezh	?	Russian, another PDP-8/? clone
	SPEAR u-LINC 100?	SPEAR, Inc, Waltham Mass (a LINC clone!)
	SPEAR u-LINC 300?	SPEAR, Inc, Waltham Mass (a LINC clone!)
	DCC-112		70-71	Digital Computer Controls
	DCC-112H	71	Digital Computer Controls
	6100 Sampler	7?	Intersil, their IM6100 promotional kit
	Intercept I	7?	Intersil, based on IM6100
	Intercept Jr	7?	Intersil, based on IM6100
	PCM-12		7?	Pacific CyberMetrix, based on Intercept bus
	PCM-12A		7?	Pacific CyberMetrix, fixed to clock at 4MHz
	SBC-8		84-88	CESI, Based on IM6120, SCSI bus
	
------------------------------

Subject: What about the LINC/8 and PDP-12?

Wesley Clark, then at Lincoln Labs, developed the LINC, or Laboratory
INstrumentation Computer, as a personal laboratory computer in the
early 1960's.  He developed it in response to the needs of Mary Brazier,
a neurophysiologist at MIT who needed better laboratory tools.  Over 24
LINC systems were built by customers before late 1964 when DEC began
selling a commercial version (see Computers and Automation, Nov. 1964,
page 43).  By the time DEC introduced the LINC-8, 43 LINC systems had
been installed (see Computers and Automation, Mar. 1966, page 34).

When Lincoln Labs decided that the LINC did not fit their mission, a
group at the the National Institute of Health funded an experiment to
see if the LINC would be a productive tool in the life sciences.  As a
result of this project, 12 LINCs were built and debugged, each by its
eventual user.

The LINC was the first 12 bit minicomputer built using DEC hardware.
Like the PDP-5 and other early DEC computers, it was built with system
modules, DEC's first family of logic modules.  Along with the CDC 160,
it paved the way for the PDP-5 and PDP-8.

When compared with the PDP-8, the LINC instruction set was not as well
suited for general purpose computation, but the common peripherals
needed for lab work such as analog-to-digital and digital-to-analog
converters were all bundled into the LINC system.  Users judged it to
be a superb laboratory instrument.

One of the major innovations introduced with the LINC was the LINCtape.
These tapes could be carelessly pocketed or dropped on the floor
without fear of data loss, and they allowed random access to data
blocks.  DEC improved on this idea slightly to make their DECtape
format, and DECtape was widely used with all DEC computers made in the
late 1960's and early 1970's.

The motives behind the development of LINCtape were the same motives
that led IBM to develop the floppy disk almost a decade later, and in
fact, DECtape survived as a widely used medium until DEC introduced the
RX01 8 inch floppy disk drive around 1975, and even after this, DECtape
was only slowly phased out.

Within a year of the introduction of the PDP-8, DEC released the LINC-8,
a machine that combined a PDP-8 with a LINC in one package.  The
success of the LINC-8 led DEC to re-engineer the machine using TTL
logic in the late 1960's; the new version was originally to be called
the LINC-8/I, but it was sold as the PDP-12.  Both the LINC-8 and the
PDP-12 had impressive consoles, with separate sets of lights and
switches for the LINC and PDP-8 halves.

The success of the LINC-8 also led to the development of a clone, the
SPEAR micro-LINC.  This machine used Motorola MECL integrated circuits
and was available for delivery in (June 1965? this date must be wrong!).

The LINC-8 and PDP-12 could run essentially any PDP-8 or LINC program,
with the exception of the few programs that relied on the primitive
interrupt structure of the original LINC architecture; on the LINC-8,
all interrupts were handled by the PDP-8 side of the hardware.  Because
the LINC-8 and PDP-12 had instructions for switching between modes, a
new body of software was developed that required both modes.

One feature of LINC and LINC-8 software is the common use of the graphic
display for input-output.  These machines were some of the first to
include such a display as a standard component, and many programs used
the knobs on the analog to digital converter to move a cursor on the
display in the way we now use a mouse.

Various versions of LAP, the Linc Assembly Program, were the dominant
assemblers used on the LINC.  WISAL (WISconson Assembly Language) or
LAP6-W was the version of this assembler that survived to run on the
PDP-12.  Curiously, this includes a PDP-8 assembler written in LINC code.

LAP6-DIAL (Display Interactive Assembly Language) evolved from this on
the PDP-12 to became the dominant operating system for the PDP-12.  The
8K version of this is DIAL MS (Mass Storage), even if it has only two
LINCtape drives.  These were eventually displaced by the OS/8 variant
known as OS/12.

------------------------------

Subject: Where can I get a PDP-8 today?

The IM6100 chip is still available (Electronic Expediters, (818)781-1910
(in North America) listed them at US$23.50 each as of 10/1994), and CESI
may still make their clone, for a high price, but you can't buy a new
DEC PDP-8.  There are quite a few PDP-8 machines to be found in odd
places on the used equipment market.  They were widely incorporated into
products such as computer controlled machine tools, X-ray diffraction
machines, and other industrial and lab equipment.  Many of them were
sold under the EduSystem marketing program to public schools and
universities, and others were used to control laboratory instrumentation.
After about 1976, Reuters bought as many as 10,000 OMNIBUS based
machines per year, with perhaps 2000 per year going to other customers.

If you can't get real hardware, you can get emulators.  Over the years,
many PDP-8 emulators have been written; the best of these are
indistinguishable from the real machine from a software prespective,
and on a modern high-speed RISC platform, these frequently outperform
the hardware they are emulating.  An emulator is available from DECUS,
catalog number RB0128; This and other emulators are available from:

  ftp://sunsite.unc.edu/pub/academic/computer-science/history/pdp-8/emulators
  ftp://ftp.cs.uiowa.edu/public/jones/pdp8/emulator.txt.Z

Finally, you can always build your own.  The textbook "The Art of
Digital Design," second edition, by Franklin Prosser and David Winkel
(Prentice-Hall, 1987, ISBN 0-13-046780-4) uses the design of a PDP-8 as
a running example.  Many students who have used this book were required
to build working PDP-8 systems as lab projects.

------------------------------

Subject: Where can I get PDP-8 documentation?

The key documents published by DEC describing each model of the PDP-8
are all out of print, and DEC was in the habit of printing much of
their documentation on newsprint with paperback bindings, which is to
say, surviving copies tend to be yellow and brittle.  DEC distributed
huge numbers of catalogs and programming handbooks in this inexpensive
paperback format, and these circulate widely on the second-hand market.
When research laboratories and electronics shops are being cleaned out,
it is still common to find a few dusty, yellowed copies of these books
being thrown out.

Douglas Jones has made a small number of bound photocopies of DEC's
1973 introduction to programming, perhaps the definitive introduction
to the PDP-8, and the other early DEC handbooks need similar treatment
before they all crumble.

Some PDP-8 refernce material has been transcribed into Hypertext format
and is available over WWW from:

	http://www.cs.uiowa.edu/~jones/pdp8/index.html

Maintenance manuals are harder to find, but more valuable.  If you need
one, you usually need to find someone willing to photocopy one of the
few surviving copies.  DEC has been friendly to collectors, granting
fairly broad letters of permission to reprint obsolete documentation,
and the network makes if fairly easy to find someone who has the
documentation you need and can get copies.  The most difficult to copy
material is the large prints, many of which would be quite useful if
photoreduced, but this is expensive.

------------------------------

Subject: What operating systems were written for the PDP-8?

A punched paper-tape library of stand-alone programs was commonly used
with the smallest (diskless and tapeless) configurations from the
beginning up through the mid 1970's.  This included a paper-tape based
text editor, the PAL III and MACRO-8 assembler, and a FORTRAN compiler,
as well as a library of support routines.  Many paper tapes from this
library survive to the present at various sites!  The minimum
configuration expected by these tapes is a CPU with 4K memory and a
teletype ASR 33 with paper tape reader and punch.  Note that much of this
paper-tape-based software is based on memory-use and I/O conventions that
are incompatible with later disk-based systems.

The DECtape Library System was a DECtape oriented save and restore system
that was available from the start.  The resident portion of this system
occupies only 17 words of memory (7600-7625 octal), and it allowed saving
and restoring absolute core images as named files on a reel of DECtape.
Initially, program development was still done with paper tape, and only
executable memory images were stored on DECtape, but eventually, a limited
DECtape-based text editor was introduced, along with a DECtape based
assembler.

The 4K Disk Monitor System provided slightly better facilities.  This
supported on-line program development and it worked with any device that
supported 129 word blocks (DECtape, the DF32 disk, or the RF08 disk).
It was quite slow, but it also used very little of the available memory.

MS/8 or the R-L Monitor System, was developed starting in 1966 and
submitted to DECUS in 1970.  This was a disk oriented system, faster than
the above, with tricks to make it run quickly on DECtape based systems.

POLY BASIC was a BASIC only system submitted to DECUS and later sold by
DEC as part of its EduSystem marketing program.  EduSystem 25 Basic
is available from:

	ftp://nickel.ucs.indiana.edu/pub/DEC/PDP8/Langs/Edu25Basic

P?S/8 was developed starting in 1971 from an MS/8 foundation.  It runs
on minimal PDP-8 configurations, supports somewhat device independant
I/O and requires a random-access device for the file system (DECtape is
random-access!).  P?S/8 runs compatibly on most PDP-8 machines including
DECmates, excepting only the PDP-8/S and PDP-5.  P?S/8 is still being
developed!

Richard F. Larry developed a system called the Fully Upward Compatible
Keyboard Monitor; and between a Wednesday and the following Friday, a
prototype was up and running from DECtape.  The original intention of
this project was to build a programming environment for the PDP-8 that
looked like TOPS-10 on the PDP-10.  A year later, this was released as
Programming System/8 (or PS/8), and then renamed OS/8 in 1971 because
Eli Glaser (a salesman from Long Island) said he could sell more systems
with an operating system than with a programming system, and because, by
renaming the system, DEC could increase the price despite Nixon's
wage-price freeze.

OS/8, developed in parallel with P?S/8, became the main PDP-8 programming
environment sold by DEC.  The minimum configuration required was 8K words
and a random-access device to hold the system.  For some devices, OS/8
requires 12K.  There are a large number of OS/8 versions that are not
quite portable across various subsets of the PDP-8 family.  OS/8 V3D was
renamed OS/78 (to match the VT78), and by the time OS/78 V3 was released,
support for Omnibus machines was no longer important.  OS/78 V4 was
developed for the DECmate I, and the name OS/278 used for the versions
released with later DECmate machines.  These have unnecessary
incompatabilities with earlier versions of OS/8.  OS/278 and related
material is available from DECUS as catalog item 800941, or from:

	ftp://ftp.telebit.com/pub/pdp8/os278
	ftp://ftp.update.uu.se/pub/pdp8
	ftp://sunsite.unc.edu/pub/academic/computer-science/history/pdp-8/os8

OS8 (no slash) may still be viable.  It requires 8K of main memory, an
extended arithmetic unit, and DECtape hardware.  Unlike most PDP-8
operating systems, it uses a directory structure on DECtape compatible
with that used on the PDP-10.

TSS/8 was developed in 1968 as a timesharing system.  It required a
minimum of 12K words of memory and a swapping device.  It was the
standard operating system on the EduSystem 50 which was sold to many
small colleges and large public school systems.  Each user gets a
virtual 4K PDP-8; many of the utilities users ran on these virtual
machines were only slightly modified versions of utilities from the
Disk Monitor System or paper-tape environments.

Other timesharing systems developed for the PDP-8 include MULTI-8, ETOS,
MULTOS, and OMNI-8; some of these required nonstandard memory management
hardware.  By the mid 1970's, some of these were true virtual machine
operating systems in the same spirit as IBM's VM-370; they typically
supported some version of OS/8 running on a 32K virtual PDP-8 assigned
to each user.  Some could support different user operating systems on
each virtual machine, others supported addressing of more than 4K for
data, but limited code to field zero of a process's virtual memory.
The source for MULTOS is available from:

	ftp://ftp.update.uu.se/pub/pdp8/multos8

CAPS-8 was a cassette based operating system supporting PAL and BASIC.
There are OS/8 utilities to manipulate CAPS-8 cassettes, and the file
format on cassette is compatible with a PDP-11 based system called
CAPS-11.

RTS/8 was a real-time system developed by DEC, developed from an earlier
system, SRT8, dating back to at least 1974.  Curiously, even the last
versions of RTS/8 continued to support paper-tape and DECtape.  Source
code for most of the versions of RTS and SRT are available from:

	ftp://sunsite.unc.edu/pub/academic/computer-science/history/pdp-8/rts8

WPS was DEC's word processing system, developed for the 8/E with a VT50
terminal with special WPS keycaps replacing the standard keycaps, and
widely used on the 1980's vintage machines.  It was heavily promoted on
the VT-78, and when the DECmates came out, DEC began to suppress knowledge
that DECmates could run anything else.  WPS-11 was a curious distributed
system using a PDP-11 as a file server for a cluster of VT-78 WPS systems.
DECmate/WPS Version 2.3 is available from DECUS for the DECmate II and
DECmate III under the catalog entry DM0114.

COS-310, DEC's commercial operating system for the PDP-8, supported the
DIBOL language.  COS-310 was a derivative of MS/8 and OS/8, but with a
new text file format.  The file system is almost the same as OS/8, but
dates are recorded differently, and a few applications can even run under
both COS and OS/8.  COS was the last operating system other than WPS
promoted by DEC for the DECmates.

------------------------------

Subject: What programming languages are supported on the PDP-8

The PAL family of assembly languages, particularly PAL III and PAL8 are
as close to a standard assembly language as can be found for the PDP-8.
These produce absolute object code and there are versions of PAL for
minimally configured machines, although these have severe symbol table
limitations.  Cross assemblers that are somewhat compatable with PAL
can be obtained from:

	ftp://ftp.cs.uiowa.edu/public/jones/pdp8/pal.c.Z
	ftp://sunsite.unc.edu/pub/academic/computer-science/history/pdp-8/emulators/gray

MACRO-8 was DEC's first macro assembly language for the PDP-8, but it
was rarely used outside the paper-tape environment.  MACREL and SABR are
assembly languages that produce relocatable output.  SABR is the final
pass for the ALICS II FORTRAN compiler (developed by ICS), and MACREL
was developed in (unfulfilled) anticipation of similar use.  MACREL was
heavily used by the DECmate group at DEC.  MACREL is available from

	ftp://ftp.update.uu.se/pub/pdp8/os8

There was also RALF, the relocatable assembler supporting RTPS FORTRAN,
and FLAP, an absolute assembler derived from RALF.  Both SABR and
RALF/FALP are assemblers that handle their intended applications but
have quirky and incompatible syntax.

A subset of FORTRAN was supported on both the PDP-5 and the original
PDP-8.  Surviving documentation describes a DEC compiler from 1964 and
a compiler written by Information Control Systems from 1968.  The
latter, ALICS II FORTRAN, was originally a paper tape based compiler,
but it forms the basis of the OS/8 8K FORTRAN compiler, and was also
adapted to the Disk Monitor System (the latter version had overlay
support that was never carried forward into more modern systems).

RTPS FORTRAN required 8K and a floating point processor; it had real-time
extensions and was a full implementation of FORTRAN IV (also known as
ANSI FORTRAN 66).  OS/8 F4 is RTPS FORTRAN stripped of the requirement
for hardware floating point (if the hardware is missing, it uses
software emulation).  A version of FORTRAN is available from

	ftp://ftp.update.uu.se/pub/pdp8/os8

FOCAL, an interpretive language comparable to BASIC, was available on
all models of the family, including the PDP-5 and PDP-8/S.  Versions of
FOCAL run under OS/8, P?S/8 and other systems, and there were many special
purpose overlays for FOCAL developed by DEC and by various users.  DEC's
later FOCAL releases for the PDP-8 included code to deliberately introduce
subtle bugs when run on a DCC 112 computer!  Various versions of FOCAL
are available from:

	ftp://nickel.ucs.indiana.edu/pub/DEC/PDP8/Langs/Focal

Many versions of BASIC were also available, from DEC and other sources.
DEC BASIC was widely used on PDP-8 systems sold under the EduSystem
marketing program.  A paper-tape version was available that ran in 4K
and was compatible with disk based systems, versions were developed for
OS/8 and TSS/8, an 8K stand-alone time-sharing version was available,
and there were others.  EduSystem 25 Basic is available from:

	ftp://nickel.ucs.indiana.edu/pub/DEC/PDP8/Langs/Edu25Basic

DIBOL was DEC's attempt at competing with COBOL in the commercial arena.
It was originally implemented under MS/8 but most versions were sold to
run under the COS operating system.

Algol was available from a fairly early date.  One version is available
from:

	ftp://nickel.ucs.indiana.edu/pub/DEC/PDP8/Langs/Algol

At least two Pascal compilers were developed for the PDP-8.  One was a
Pascal-S interpreter, written in assembler, the other was a Pascal-P
compiler with a P-code interpreter written in assembler.

A LISP interpreters was written for the PDP-8; the original version
ran in 4K (originally written in Germany?); a disassembled and commented
version of this was the basis of expanded versions that eventually
could utilize up to 16K.  One version of LISP is available from:

	ftp://nickel.ucs.indiana.edu/pub/DEC/PDP8/Langs/Lisp

A Pascal S interpreter, requiring a 28K PDP-8/E configuration, is available
from:

	ftp://nickel.ucs.indiana.edu/pub/DEC/PDP8/Langs/Pascal

POLY SNOBOL was a version of SNOBOL that was somewhere between
Griswold's definitions of SNOBOL 3 and SNOBOL 4.

TECO, the text editor, is available, and is also a general purpose
language, and someone is working on a PDP-8 C.  The story of TECO on the
PDP-8 is convoluted.  Russ Ham implemented TECO under his OS8 (without
a slash) system.  This version of TECO was pirated by the Oregon Museum
of Science and Industry (OMSI), where the system was ported to PS/8.
Richard Lary and Stan Rabinowitz made it more compatible with other
versions of TECO, and the result of this work is the version distributed
by DECUS (catalog number 110450 is the manual).  RT-11 TECO for the
PDP-11 is a port of this code.

DECUS also lists the PAGE8 language (catalog numbers 800936), the VISTA
editor (catalog number 800938), and the ICE text editor (catalog number
800939).

------------------------------

Subject: Where can I get PDP-8 software?

DEC is still making computers, but they've largely forgotten about the
PDP-8.  The main DEC WWW server is

	http://www.digital.com/

DECUS, the DEC User Society, is still alive and well, and their submission
form still lists PAL8 and FOCAL as languages in which they accept
submissions!  The DECUS library catalog is available on-line at
decus.org; www access is through gopher.decus.org or

	http://www.decus.org/

To quote the README file from the DECUS on-line catalog, "Items from
older DECUS Library catalogs are still also available (provided their
media can still be read), but machine readable catalog information is
not available for these."  Direct questions by E-mail to
[email-masked].

The following anonymous FTP sites contain publically accessable archives
of PDP-8 software and other information:

	ftp://ftp.telebit.com/pub/pdp8
	ftp://ftp.update.uu.se/pub/pdp8
	ftp://nickel.ucs.indiana.edu/pub/DEC/PDP8
	ftp://sunsite.unc.edu/pub/academic/computer-science/history/pdp-8

The latter archive also maintains an archive of traffic in alt.sys.pdp8
in the directory ...pdp8/usenet and an archive of traffic in the
pdp8-lovers mailing list in .../pdp8/pdp8-lovers.

The archive at Indiana contains source code for many PDP-8 compilers and
interpreters, as well as common utilities and games.

------------------------------

Subject: Where can I get additional information?

The file WHAT-IS-A-PDP8, by Charles Lasner contains considerable
additional information; this file is available by ftp from:

	ftp://ftp.telebit.com/pub/pdp8/WHAT-IS-A-PDP8

This file gives details of every PDP-8 model including the small quirks
and incompatabilities that (to be generous) allow software to determine
which model it is running on.  These quirks also make it all too easy
for careless programmers to write almost portable software with very
obscure bugs.

The mailing list [email-masked] reaches a number of PDP-8 owners
and users, not all of whom have USENET feeds.  The USENET newsgroup
alt.sys.pdp8 needs to be gatewayed to this mailing list.

Many "archival" books have included fairly complete descriptions of the
PDP-8; among them, "Computer Architecture, Readings and Examples" by
Gordon Bell and Allen Newell is among the most accurate and complete
(but difficult to read).

------------------------------

Subject: What use is a PDP-8 today?

What use is a Model T today?  Collectors of both come in the same basic
classes.  First, there are antiquarians who keep an old one in the
garage, polished and restored to new condition but hardly ever used.
Once a year, they warm it up and use it, just to prove that it still
works, but they don't make much practical use of it.

PDP-8 systems maintained by antiquarians are frequently in beautiful
shape.  Antiquarians worry about dust, chipped paint, and missing
switches, and they establish newsgroups and mailing lists to help them
locate parts and the advice needed to fix their machines.

In the second class are those who find old machines and soup them up,
replacing major parts to make a hotrod that only looks like the original
from the outside, or keeping the old mechanism and putting it to uses
that were never intended.  Some PDP-8 owners, for example, have built
PDP-8 systems with modern SCSI disk interfaces!  There is serious
interest in some quarters in constructing an omnibus board that would
support an IDE disk of the variety that was mass-produced for the
IBM PC/AT.

Last, there are the old folks who still use their old machines for their
intended purposes long after any sane economic analysis would recommend
such use.  If it ain't broke, don't fix it, and if it can be fixed,
why bother replacing it?  Both Model T Fords and the classic PDP-8
machines are simple enough that end users can maintain and repair them
indefinitely.  All you need to keep a vintage -8 running are a stock
of inexpensive silicon diodes and a stock of 2N3639B or better,
2N3640 transistors.

Unlike most modern personal computers, PDP-8 systems were routinely sold
with complete maintenance manuals; these included schematic diagrams,
explanations of not only how to use the devices, but how they are built,
and suggestions to those considering building their own peripherals.
Compared with many so-called "open systems" of today, the PDP-8 was far
better documented and far more open.

Preservation of the PDP-8 has proven to be of immense practical value
in defending against the rising tide of patents in the area of
interactive graphics.  For example, when Magnavox sued Nintendo
for half a billion dollars, a documented copy of a ping pong game,
written on a LINC back in the early 1960's, was crucial to the proof
that computer games predated the Magnavox patent by over 5 years.
The fact that this can be run today on a surviving LINC-8 makes
demonstrating this proof far easier than if the only surviving relic
was a dusty listing.

Finally, the PDP-8 is such a minimal machine that it is an excellent
introduction to how computers really work.  Over the years, many students
have built complete working PDP-8 systems from scratch as lab projects,
and the I/O environment on a PDP-8 is simple enough that it is a very
appropriate environment for learning operating system programming
techniques.

------------------------------

Subject: Who's Who?

C. Gordon Bell is generally credited with the original design of the
PDP-8.  He was also involved with recommending what became the PDP-11
when that design was competing with the design that probably became the
NOVA, and as vice president of research, he oversaw the development of
the DEC VAX family.

Alan Kotok worked with Bell in working up the original specifications
of the PDP-8.

Ben Gurley designed most of the big DEC machines, starting with the
PDP-1.  The actual design work on the -8, however, was done by Ed
deCastro, who later founded Data General to build the Nova.

Ken Olson ran DEC from the beginning.

Ed Yourdon, who later became well known as a programming methodology
guru, helped hack up the PAL III assembler for the -8 from PAL II.

Richard Merrill invented FOCAL and wrote the original (1968) and classic
FOCAL-69 interpreters for the PDP-8.  He also did early translations of
the interpreter to PDP-7/PDP-9 code and perhaps the earliest PDP-11
version.  In addition, he wrote the EDIT-8 paper-tape based text editor
based on the FOCAL built-in text editor.

Richard F. Lary developed OS/8, with help from Ed Friedman and another
programmer named Paul, under the management of Chuck Conley.

Charles Lasner developed P?S/8, and he is widely known as a leader in
the movement to preserve these historic machines.  He created the
alt.sys.pdp8 newsgroup.

Wesley Clark developed the LINC while working at Lincoln Labs; this was
the first 12 bit minicomputer built with DEC parts.

Mary Allen Wilkes Clark developed the early LAP programs for the LINC.

Douglas W. Jones wrote this FAQ, but prior to the summer of 1992, he'd
never used a PDP-8.  He has also written a report on how to photocopy
and archivally bind ailing paperback books such as DEC's handouts, a
PAL-like cross assembler in C, and a UNIX-based PDP-8 emulator.

------------------------------

End of PDP-8 Frequently Asked Questions (posted every other month)
******************************************************************

Article 1116 of alt.sys.pdp8:
Path: bigblue.oit.unc.edu!concert!theo!news-server.ncren.net!taco.cc.ncsu.edu!gatech!swrinde!pipex!uunet!news.uiowa.edu!news
From: [email-masked] (Douglas W. Jones)
Newsgroups: alt.sys.pdp8,alt.answers,news.answers
Subject: PDP-8 Summary of Models and Options (posted every other month)
Followup-To: alt.sys.pdp8
Date: 8 Dec 1994 08:08:08 GMT
Organization: Computer Science, University of Iowa, Iowa City, Iowa, USA
Lines: 1317
Approved: [email-masked]
Distribution: world
Expires: 8 Feb 1995 08:08:08 GMT
Message-ID: <[email-masked]>
NNTP-Posting-Host: pyrite.cs.uiowa.edu
Summary: Descriptions of all models of the DEC PDP-8 computer.
	Those posting to alt.sys.pdp8 should read this.
Keywords: FAQ DEC PDP 8
Xref: bigblue.oit.unc.edu alt.sys.pdp8:1116 alt.answers:5909 news.answers:32285

Archive-name: dec-faq/pdp8-models
Last-modified: Oct 11, 1994

Frequently Asked Questions about DEC PDP-8 models and options.

	By Douglas Jones, [email-masked]
	(with help from many folks)

Sites known to carry FTPable copies of this file:

	ftp://rtfm.mit.edu/pub/usenet/alt.sys.pdp8
        ftp://ftp.uu.net/usenet/news.answers/dec-faq
	ftp://src.doc.ic.ac.uk:/pub/usenet/news.answers/alt.sys.pdp8
	ftp://sunsite.unc.edu/pub/academic/computer-science/history/pdp-8/docs

Automatic translations of this document to HTML format (as used by World Wide
Web) are available from:

        http://www.cis.ohio-state.edu/hypertext/faq/usenet/dec-faq/top.html

This posting conforms to RFC1153 USENET digest format (with exceptions due
to the fact that it is not really a digest).

The purpose of this document is to supplement the material in the primary
"Frequently Asked Questions about the PDP-8" file with more detailed
information about the hardware and options of the different models of the
PDP-8 sold by DEC.

Although this document is something of a history of the DEC PDP-8 family,
the primary purpose of this document is as a guide and general outline to
the PDP-8 models and options likely to be encountered by those involved
in collecting and restoring such systems.

Contents:

	What is a PDP-5?
	What is a PDP-8?
	What is a LINC-8?
	What is a PDP-8/S?
	What is a PDP-8/I?
	What is a PDP-8/L?
	What is a PDP-12?
	What is a PDP-8/E?
	What is a PDP-8/F?
	What is a PDP-8/M?
	What is a PDP-8/A?
	What is a VT78?
	What is a DECmate I?
	What is a DECmate II?
	What is a DECmate III?
	What is a DECmate III+?

----------------------------------------------------------------------

Subject: What is a PDP-5?

Date of introduction:  Aug 11, 1963, unveiled at WESCON.
Date of withdrawal:    early 1967.
Total production run:  116.
Price: $27,000

Technology:  The PDP-5 was built with DEC System Modules, the original
	line of transistorized logic modules sold by DEC.  The supply
	voltages were +10 and -15 volts, with logic levels of -3 (logic 1)
	and 0 (logic 0).  Logic was packaged on boards that were about
	4.75 inches high with each card mounted in a metal frame with a
	22 pin edge connector.

	Input output devices were connected to the daisy-chained I/O bus
	using military-style armored cables and connectors.  Use of
	toggle switches (as opposed to slide switches) on the front
	panel was another vestige of military-style design.

Reason for introduction:  This machine was inspired by the success of
	the CDC-160, Seymour Cray's 12 bit minicomputer, and by the
	success of the LINC, a machine that was built by DEC customers
	out of System modules.  These demonstrated that there was a
	market for a small inexpensive computer, and from the start,
	DEC's advertisements were aimed at this market.  "Now you can
	own the PDP-5 computer for what a core memory alone used to
	cost: $27,000", ran one 1964 ad.

Reason for withdrawal:  The PDP-8 outperformed the PDP-5, and did so for
	a lower price.

Compatability:  The core of the PDP-8 instruction set is present, but
	memory location zero is the program counter, and interrupts are
	handled differently.  The Group 1 OPR rotate instructions cannot
	be combined with IAC or CMA; this limits the ability of the
	PDP-5 to support code from later models.

The machine does not support 3 cycle data-break (DMA transfers using
	memory to hold buffer address and word-count information), so
	many later PDP-8 peripherals can not be used on the PDP-5.  In
	addition, DMA transfers are not allowed outside the program's
	current 4K data field, severely limiting software compatability
	on systems with over 4K of memory where either interrupts or
	software initiated changes to the data field during a transfer
	would cause chaos.

Standard configuration:  CPU with 1K or 4K of memory (2K and 3K versions
	were not available).

Peripherals:
	An extended arithmetic element (EAE) was available; this was an
	I/O device, using IOT instructions to evoke EAE operations.  As
	a result, it was not compatable with the later PDP-8 EAEs.  In
	addition, machines with the EAE option had a different front
	panel from those without.

	The type 552 DECtape control and type 555 dual DECtape transports
	were originally developed for the PDP-5 and contemporaneous DEC
	systems such as the PDP-6.

	After the PDP-8 was introduced, DEC offered a bus converter that
	allowed the PDP-5 to support standard PDP-8 negibus ueripherals,
	so long as they avoided using 3-cycle data break transfers.  The
	standard 804 PDP-8 expander box was frequently sold as an
	upgrade to PDP-5 systems.

Survival:  Do any PDP-5 systems survive?

------------------------------

Subject: What is a PDP-8?

Date of introduction:  1965 (Unveiled March 22, in New York).
Date of withdrawal:    1968.
Total production run:  1450.
Also known as:
	Classic PDP-8 (to point out lack of a model suffix)
	Straight-8 (Again, points out the lack of a model suffix)
	PCP-88, an OEM label, used by Foxboro Corporation.
Price: $18500

Technology:  Mostly standard DEC R-series logic modules; these were
	originally discrete component transistor logic, but around the
	time the PDP-8 was introduced, DEC introduced the Flip Chip, a
	hybrid diode/resistor "integrated circuit" on a ceramic substrate.
	These could directly replace some of the discrete components on
	some logic modules, and DEC quickly began to refer to all R-series
	modules as flip-chip modules; they even advertised the PDP-8 as
	an integrated circuit computer.  A typical flip-chip module, the
	R111, had three 2-input nand gates and cost $14, with no price
	change from 1965 to 1970.  Some special dual height R-series
	modules were designed specifically for the PDP-8.

	S and B-series logic modules were also used; these are similar
	to their R-series cousins, but with different speed/fanout
	tradeoffs in their design.  Some logic modules have trimmers
	that must be tuned to the context, making replacement of such
	modules more complex than simply swapping boards.

	As with the system modules used in the PDP-5, the supply
	voltages were +10 and -15 volts and the logic levels were -3
	(logic 1) and 0 (logic 0).  Logic was packaged on boards that
	were 2.5 inches wide by 5 inches long.  The card edge connector
	had 18 contacts on 1/8 inch centers.  Some double height cards
	were used; these had two card edge connectors and were 5 1/8
	inches high.  Machine wrapped wire-wrap technology was used on
	the backplane using 24-gauge wire.

	The "negibus" or negative logic I/O bus used -3 and 0 volt logic
	levels in 92 ohm coaxial cable, with 9 coaxial cables bundled
	per connector card and 6 bundles making up the basic bus.  5
	(later 4) more bundles were required to support data-break (DMA)
	transfers.  The total bus length was limited to 50 feet, and bus
	termination was generally kluged in with 100 ohm resistors
	clipped or wrapped into the backplane, although a bus terminator
	card was sometimes used.  Some time after the first year of
	production, flat ribbon cable made of multiple coaxial cables
	was used, and later still, shielded flat stripline cable was used
	(but this cut the allowed bus length by a factor of two).

	Core memory was used, originally made by FERROXCUBE, with a 1.5
	microsecond cycle time, giving the machine an add time of 3
	microseconds.  4K of core occupied an aluminum box 6 inches on a
	side and needed numerous auxiliary flip-chips and for support,
	as well as an array of boards from the core vendor.  It is worth
	noting that the PDP-8 was about as fast as was practical with the
	logic technology used; only by using tricks like memory
	interleaving or pipelining could the machine have been made much
	faster.

Reason for introduction:  This machine was inspired by the success of
	the PDP-5 and by the realization that, with their new Flip-Chip
	technology, DEC could make a table-top computer that could be
	powered by a single standard wall outlet; of course, adding any
	peripherals quickly increased the power requirement!

Reason for withdrawal:  The PDP-8/I was less expensive, and after
	initial production difficulties, it equalled the performance of
	the PDP-8.

Compatability:  This machine defines the core of the PDP-8 instruction
	set, but with restrictions that were lifted on later machines.
	The Group 1 OPR instruction IAC cannot be combined with any of
	the rotate instructions.  If RAR and RAL or RTR and RTL are
	combined, the results are unpredictable (simultaneous set and
	reset of bits of AC results in metastable behavior).  The IOT 0
	instruction was used for the internal type 189 ADC, and not for
	the later CAF (clear all flags) instruction.  As a result, if
	the ADC option was not present, IOT 6004 (or microcoded
	variants) would hang the machine.

	The SWP instruction (exchange AC and MQ) never works, even if
	the extended arithmetic element is present.  This works on later
	models when the EAE is present, although it was only documented
	with the introduction of the PDP-8/E.  Finally, the EAE lacks
	the SCL (shift count load) instruction that is present on later
	models.

	On machines with 8K or more, an attempt to change the data field
	to a non-existant field caused a bizarre double-indirect and
	skip instruction execution that must be accounted for in memory
	diagnostics.

Standard configuration:  The PDP-8 was sold as a CPU with 4K of memory,
	a 110 baud current loop teletype interface and an ASR 33 Teletype.
	In addition, the standard in-cabinet logic includes support for
	the full negibus interface, including data-break (DMA) transfers.

	Both a rack-mount model with rosewood trim and an elegant
	plexiglass enclosed table-top configuration were standard.  Under
	the skin, the basic machine occupies a volume 33 inches high by
	19 inches wide by 22 inches deep.  The two halves of the backplane
	are mounted vertically, like the covers of a book, with the
	spine in back and circuit modules inserted from the two sides.
	Sliding the CPU out of the relay rack or removing the plexiglass
	covers allows the backplane to swung open to access the wires-wrap.

Expandability:  In-cabinet options include the type 182 extended
	arithmetic element (EAE), the type 183 memory extension control
	subsystem, and the type 189 low performance analog to digital
	converter (ADC).  Prewired backplane slots were reserved for
	all of these.

	Expansion beyond 4K of memory requires rack space for the
	rack-mounted type 184 memory module; each such module adds one
	4K field of memory, up to a maximum of 32K.  The rack-mount CPU
	occupied a large part of one rack, allowing room for a single
	type 184 memory expansion module below the CPU; generally, a
	second rack was needed for added peripherals or memory.

	At the end of the production run, some PDP-8 systems were sold
	with PDP-8/I memory, allowing room for an additional 4K without
	need for an expansion chassis.  These nonstandard machines were
	very difficult to maintain!

Peripherals:  At the time of introduction, the following negibus
	peripherals were offered.

	-- Type 750C high speed paper tape reader and control.
	-- Type 75E high speed paper tape punch and control.
	-- Type 138E analog to digital converter.
	-- Type 139E analog multiplexor.
	-- Type 34D oscilloscope display control (dual digital to analog).
	-- Type 350B incremental (CalComp) plotter control.
	-- Type 451 card reader and control.
	-- Type 450 card punch control for IBM Type 523 punch.
	-- Type 64 (later 645) Mohawk line printer and control.
	-- Type RM08 serial magnetic drum system (up to 256K words).
	-- Type 552 DECtape control (for type 555 DECtape drives).
	-- Type 57A magnetic tape control (IBM type 729 drive).
	-- Type 580 magnetic tape system.

	By 1966, the following peripherals had been added to the line:

	-- Type AA01A three-channel digital to analog converter.
	-- Type CR01C card reader control.
	-- Type TC01 DECtape control for up to 8 TU55 transports.
	-- Type 251 drum (8-256 tracks, 8 sectors/track, 128 words/sector).
	-- Type 645 line printer control.
	-- Type 680 data communications system (allows 64 teletypes).

	By 1967, the following peripherals had been added to the line:

	-- Type AF01 analog to digital converter and multiplexor.
	-- Type AX08 parallel digital input port.
	-- Type 338 Programmed Buffered Display (vector graphics).

	By 1968, the following new peripheral had been added:

	-- Type DF32 fixed head disk system (32K to 256K words).
	-- Type BE01 OEM version of the TC01 (no blinking lights).
	-- Type BE03 dual TU55 drive for the TC01 or BE01.

	Finally, as DEC abandoned the negibus, they introduced the
	DW08B negibus to posibus converter so newer posibus
	peripherals could be used on older negibus machines, and the
	DW08A posibus to negibus converter to allow use of old
	peripherals on new machines.

Survival:  Many classic PDP-8 systems survive to this day

------------------------------

Subject: What is a LINC-8?

Date of introduction:  1966 (during or before March).
Date of withdrawal:    1969
Total production run:  142.
Price: $38,500

Technology:  DEC Flip Chip modules, as in the PDP-8, with a LINC CPU
	partially reimplemented in Flip Chips and partially emulated
	with PDP-8 instructions.  (The original LINC was built from
	the same System Modules used in the PDP-5.)

Compatability:  The PDP-8 part of the machine was identical to the PDP-8.

Reason for withdrawal:  The PDP-12 accomplished the same goals at a lower
	cost.

Standard configuration:  The combined PDP-8/LINC CPU, plus 4K of memory
	was central to the system.  The set of peripherals bundled with
	the machine was impressive:

	-- An ASR 33 Teletype modified for the LINC character set.
	-- Two LINCtape drives.
	-- 8 analog to digital converter channels with knob inputs.
	-- Another 8 ADC channels with jack inputs.
	-- 6 programmable relay outputs, good up to 60 Hz.
	-- 1 Tektronix 560 oscilliscope, somewhat modified.

	The X and Y axis control for the scope came from DACs attached
	to the LINC's AC and MB registers, respectively.

Expandability:

	In addition to standard PDP-8 peripherals, up to 3 additional
	pairs of LINCtape drives could be added, for a total of 8 drives.
	The design of the type 555 dual DECtape transport was based on
	that of the LINCtape drive.

	Up to 2 additional ranks of 8 ADC channels could be added.

	Remote oscilliscope could be added.

Survival:  One LINC-8 is known to be in operable condition today.

------------------------------

Subject: What is a PDP-8/S?

Date of introduction:  1966 (Unveiled, Aug 23, WESCON, Los Angeles).
Date of withdrawal:    1970.
Total production run:  1024.
Price: $10,000

Technology:  DEC Flip Chip modules and core memory, as in the PDP-8.
	Unlike the PDP-8, the PDP-8/S memory module was mounted between
	a pair of quad-height single-width boards that plugged into the
	standard flip-chip sockets (this was sold separately as the H201
	core memory unit, at $2000 for 4K by 13 bits).

Reason for introduction:  This machine was developed as a successful
	exercise in minimizing the cost of the machine.  It was the
	least expensive general purpose computer made with second
	generation (discrete transistor) technology, and it was one of
	the smallest such machines to be mass produced (a number of
	smaller machines were made for aerospace applications).  It was
	also incredibly slow, with a 36 microsecond add time, and some
	instructions taking as much as 78 microseconds.  By 1967, DEC
	took the then unusual step of offering this machine for off the
	shelf delivery, with one machine stocked in each field office
	available for retail sale.

Reason for withdrawal:  The PDP-8/L vastly outperformed the PDP-8/S, and
	and it did so at a lower price.

Compatability:  The core of the PDP-8 instruction set is present, but
	there are a sufficient number of incompatabilities that, as with
	the PDP-5, many otherwise portable "family of 8" programs will
	not run on the PDP-8/S.  Perhaps the worst incompatability is
	that the Group 1 OPR instruction CMA cannot be combined with any
	of the rotate instructions; as with the PDP-8, IAC also cannot
	be combined with rotate.

Standard configuration:  CPU with 4K of memory, plus PT08 110 baud current
	loop teletype interface and teletype.  Both a rack-mount and
	table-top versions were sold (both 9" high by 19" wide by 20"?
	deep).  The rack mount version included slides so it could be
	pulled out for maintenance.

Expandability:  The CPU supported the standard PDP-8 negibus, but I/O
	bandwidth was 1/5 that of the PDP-8.  Thus, most, but not all
	PDP-8 peripherals could be used.  A few DEC peripherals such as
	the DF32 came with special options such as interleaving to slow
	them down for compatability with the PDP-8/S.  The speed problems
	were such that there was never any way to attach DECtape to this
	machine.

Survival:  Because they were so slow, PDP-8/S systems were quickly
	discarded as newer machines became available for comparable prices;
	thus, they are less common today than the Classic PDP-8, even
	though comparable numbers were made.  A few survive in working
	condition.

------------------------------

Subject: What is a PDP-8/I?

Date of introduction:  1968 (announced before December '67)
Date of withdrawal:    1971.
Total production run:  3698.

Technology:  DEC M-series logic modules, called M-series flip-chips
	as the term flip-chip was applied to the module format instead
	of to DEC's hybrid integrated circuits.  M-series modules used
	TTL chips, with a +5 volt supply, packaged on the same board
	format used with the original flip-chips, but with double-sided
	card-edge connectors (36 contacts instead of 18).  Modules were
	limited to typically 4 SSI ICs each.  The M113, a typical
	M-series module, had 10 2-input nand gates and cost $23 in 1967
	(the price fell to $18 in 1970).  Wire-wrapped backplanes used
	30-gauge wire.

	The PDP-8/I, as originally sold, supported the then-standard
	PDP-8 negibus.  4K words of core were packaged in a 1 inch thick
	module made of 5 rigidly connected 5 by 5 inch two-sided printed
	circuit boards.  Connectors and support electronics occupied an
	additional 32 backplane slots.

	Nominally, the core memory (which, curiously, used a negative
	logic interface!) was supposed to run at a 1.5 microsecond cycle
	time, but many early PDP-8/I systems were delivered running at a
	slower rate because of memory quality problems.  DEC went through
	many vendors in the search for good memory!  The memory interface
	was asynchronous, allowing the CPU to delay for slow memory.  DEC
	continued to make the classic PDP-8 until the problems with
	memory speed were solved.

Reason for introduction:  This machine was developed in response to the
	introduction of DIP component packaging of TTL integrated
	circuits.  This allowed a machine of about the same performance
	as the original PDP-8 to fit in about half the volume and sell
	for a lower price.

Reason for withdrawal:  The PDP-8/E made slight performance improvements
	while undercutting the price of the PDP-8/I.

Compatability:  The core of the PDP-8 instruction set is present, and
	unlike the original PDP-8, IAC can be combined with rotate in a
	single microcoded Group 1 OPR instruction.  Combined RAR and RAL
	or RTR and RTL produce the logical and of the expected results
	from each of the combined shifts.

	If the extended arithmetic element is present, the SWP (exchange
	AC and MQ) instruction works, but this was not documented.

	On large memory configurations, memory fetches from a nonexistant
	memory field take about 30 microseconds (waiting for a bus
	timeout) and then they return either 0000 or 7777 depending on
	the memory configuration and the field that was addressed.

	A front panel bug prevented continue after load-address without
	first clearing the machine.

Standard configuration:  CPU with 4K of memory, plus 110 baud current
	loop teletype interface.  Pedestal, table-top and rack-mount
	versions were made.  The pedestal mounted version was futuristic
	looking; the table-top version split the pedistal, with the CPU
        on the table and the power supply (the base of the pedistal) on
	the floor beside the table.  The standard rack-mounted version
	had the power supply bolted to the right side of the rack while
	the CPU, mounted on slides, slid out of the left side of the rack.

Expandability: 4K of memory could be added internally, and additional
	memory could be added externally using a rack-mounted MM8I memory
	expansion module for each 4K or 8K addition over 8K.

	The backplane of the PDP-8/I was prewired to hold a Calcomp
	plotter interface, with the adjacent backplane slot reserved
	for the cable connection to the plotter.  There may be other
	built-in options.

	Initially, the CPU was sold with bus drivers for the PDP-8
	negibus, allowing this machine to support all older DEC
	peripherals, but later machines were sold with posibus interfaces,
	and many older machines were converted in the field.

	A posibus to negibus converter, the DW08A, allowed use of all
	older PDP-8 peripherals, with small modifications.  The change
	from negibus to posibus during the period of PDP-8/I production
	leads to confusion because surviving CPUs and peripherals may
	have any of three I/O bus configurations: Negibus, early posibus,
	or final posibus.  The early posibus used the same connectors
	and cables as the negibus, with only 9 conductors per connector,
	while the final posibus used both sides of the connector paddles
	for 18 bus lines per connector.  Y-shaped cables for converting
	from one physical bus layout to the other were available.  To
	add to this confusion, some negibus PDP-8/I systems were rewired
	to use 18 conductor posibus cables with negative logic!

	Eventually, an add-on box was sold that allowed PDP-8/E (OMNIBUS)
	memory to be added to a PDP-8/I.  Additionally, Fabritek sold a
	24K memory box for the 8/I and PDP-12.

Survival:  Many PDP-8/I systems are in operating condition.

------------------------------

Subject: What is a PDP-8/L?

Date of introduction:  1968 (announced before August '68)
Date of withdrawal:    1971.
Total production run:  3902.
Price: $8,500

Technology:  DEC M-series flip Chip modules, as in the PDP-8/I, with the
	same core memory as the 8/I, but with a memory cycle cycle of 1.6
	microseconds to avoid the speed problems that plagued early -8/I
	systems.

	The positive I/O bus, or posibus, was a 100 ohm bus clamped
	between 0 and 3 volts with TTL drivers and receivers.  This was
	packaged with 18 signal lines per 2-sided interconnect cable,
	using double-sided shielded mylar ribbon cable in most cases.
	Electrically, coaxial cable could be used, but the slots in the
	CPU box were too small for this.

Reason for introduction:  This machine was developed as a moderately
	successful exercise using M-series logic to produce a lower cost
	but moderately fast machine.  The idea was to cut costs by
	limiting provisions for expansion.

Reason for withdrawal:  The PDP-8/E made performance improvements while
	slightly undercutting the price of the PDP-8/L.

Compatability:  The core of the PDP-8 instruction set is present, but
	all Group 3 OPR instructions are no-ops, even the Group 3 version
	of the CLA instruction.  This is because there was no provision
	made for adding an EAE to this machine.  Microcoding RAR and RAL
	together works as in the PDP-8/I.  Finally, a new front panel
	feature was added, the protect switch.  When thrown, this makes
	the last page of the last field of memory read-only (to protect
	your bootstrap code).

	The instruction to change the data field on an 8/L becomes a
	no-op when the destination data field is non-existant; on all
	other machines, attempts to address non-existant fields are
	possible.  One option for expanding the 8/L was to add a box that
	allowed 8/E memory modules to be added to the 8/L; when this
	was done, access to nonexistant data fields becomes possible and
	always returns 0000 on read.

Standard configuration:  A CPU with 4K of memory, plus 110 baud current
	loop teletype interface was standard.  Both rack-mount and
	table-top versions were sold (both 9" high by 19" wide by 21"
	deep).  The backplane was on top, with modules plugged in from
	the bottom.  The rack-mount version could be slid out for
	maintenance.

Expandability:  The CPU supported a new bus standard, the PDP-8 posibus.
	There is little space for in-box peripherals, but an expander
	box with the same volume as the CPU was available, the BA08A;
	this was prewired to hold an additional 4K of memory and to
	support in-box peripheral interfaces for such devices as a
	Calcomp plotter interface, a card-reader interface, a 4 line
	asynch terminal interface, a real-time clock, and more.

	DEC eventually offered the BM12L, an 8K expansion box that is
	essentially the same as the MM8I, but using positive logic and
	thus incompatable with the -8/I and -12.  This allowed a total
	memory of 12K on a PDP-8/L.  This contains precisely the modules
	needed to upgrade a 4K PDP-8/I or PDP-12 to an 8K machine, or to
	populate an MM8I box to add 8K of additional memory to an 8/I or
	PDP-12.

	Finally, DEC eventually offered a box allowing PDP-8/E (OMNIBUS)
	memory to be used with the PDP-8/L.  PDP-8/L configurations with
	over 8K of memory were awkward because the front panel only
	showed one bit of the extended memory address.  As a result,
	extra lights and switches for the additional bits of the memory
	address were mounted on the front of the memory expander boxes
	for the large configurations.

	A variety of posibus peripherals were introduced, most of which
	were built with the option of negibus interface logic (the -P
	and -N suffixes on these new peripherals indicated which was
	which).  Many early PDP-8/L systems were sold with DW08A bus
	level converters to run old negibus peripherals.

	Posibus peripherals introduced after the PDP-8/L (and also used
	with posibus versions of the PDP-8/I) included:

	-- The TC08 DECtape controller (for 8 TU55 or 4 TU56).
	-- The DF32D fixed head disk controller (a posibus DF32).
	-- The FPP-12 floating point processor.
	-- The TR02 simple magnetic tape control.
	-- The RK08 disk subsystem, 4 disk packs, 831,488 words each.

Survival:  Many PDP-8/L systems are in operating condition.

------------------------------

Subject: What is a PDP-12?

Date of introduction:  1969 (February or earlier).
Date of withdrawal:    1973.
Total production run:  3500?
Price: $27,900

Technology:  DEC M-series flip Chip modules, as in the PDP-8/I.

Reason for introduction:  This machine was developed as a follow-up to
	the LINC-8.  Originally it was to be called the LINC-8/I, but
	somehow it got its own number.  In effect, it was a PDP-8/I with
	added logic to allow it to execute the LINC instruction set.

Reason for withdrawal:  The LAB-8/E and the LAB-11 (a PDP-8/E and a
	PDP-11/20 with lab peripherals) eventually proved the equal of
	the PDP-12 in practice, and LINC compatability eventually proved
	to be of insufficient value to keep the machine alive in the
	marketplace.
		
Compatability:  This machine is fully compatable with the PDP-8/I, with
	additional instructions to flip from PDP-8 mode to LINC mode and
	back.  IOT 0 could enable the API, causing trouble with later
	PDP-8 code that assumes IOT 0 is "Clear all flags".  Also, the
	DECtape instruction DTLA (6766) becomes part of a stack-oriented
	extension to the instruction set, PUSHJ, on late model (or field
	updated) machines with the KF12-B backplane.

	The PDP-12 supported trapping of those LINC functions that were
	emulated by software on the LINC-8.  This allowed it to run many
	LINC-8 bootable systems (but not all, due mostly incompatabilities
	in LINKtape support), and it allowed such things as emulation of
	LINKtape instructions for reading and writing disk.

	The TC12F Linktape controller could, with appropriate software,
	read or write DECtape.  This support is unreliable, and is not
	software compatable with the TC01 or TC08 DECtape controller.

Standard configuration:  PDP-8/LINC CPU with 4K of memory, plus 110 baud
	current loop interface, plus output relay registers.  In
	addition, the standard configuration included either two TU55 or
	one TU56 drive, with a PDP-12 only controller allowing it to
	handle LINCtape.  In addition, a 12" scope was always included,
	with a connector that can connect to a second scope.

Expandability:  An analog to digital converter and multiplexor was needed
	to fully support knob-oriented LINC software.

	Other options included:

	-- the KW12 programmable lab clock.
	-- additional TU55 or TU56 drives (up to 8 transports).
	-- the BA12 expander box
	-- the PC05 paper tape reader punch (needs the BA12).

	Fabritek made a 24K memory box that could be added to a PDP-8/I or
	PDP-12.

Survival:  A few PDP-12 systems are in operating condition.

------------------------------

Subject: What is a PDP-8/E?

Date of introduction:  1970 (during or before August).
Date of withdrawal:    1978.
Also known as:
	Industrial-8 (with a red color scheme)
	LAB-8/E (with a green color scheme)
Price: $7,390

Technology: SSI and MSI TTL logic were used on these boards, and the
	entire CPU fit on 3 boards.  Nominally, these were DEC M-series
	flip Chip modules, but in a new large format, quad-high (10.5
	inch), extended-length (9 inch, including card-edge connector,
	excluding handles).  The terms used for board height and length
	are based on the original working assumption that all flip-chips
	were plugged horizontally into a vertially mounted card-edge
	connector.  On the PDP-8/E, the cards were plugged vertically
	down into a horizontally mounted connector, so many users
	incorrectly refer to these boards as quad-wide double-high.

	Interconnection between boards was through a new bus, the OMNIBUS.
	This eliminated the need for a wire-wrapped backplane, since all
	slots in the bus were wired identically.  A new line of peripheral
	interfaces was produced, most being single cards that could be
	plugged directly into the inside the main enclosure.  These
	included a set of posibus adapters allowing use of older
	peripherals on the new machine.

	Interboard connectors were needed for some multiboard options,
	including the CPU and memory subsystems.  These used standard
	36-pin backplane connectors on the opposite side of the board
	from the backplane.  Some boards, notably memory boards, had a
	total of 8 connector fingers, 4 for the omnibus and 4 for
	interboard connectors.

	The core memory cycle time was 1.2 or 1.4 microseconds, depending
	on whether a read-modify-write cycle was involved (a jumper would
	slow all cycles to 1.4 microseconds).  A 4K core plane was
	packaged on a single quad-wide double-high board, with most of
	the drive electronics packed onto two adjacent boards.  Soon after
	the machine was introduced, an 8K core plane was released in the
	same format.

Reason for introduction:  The cost of the PDP-8/I and PDP-8/L was
	dominated by the cost of the interconnect wiring, and this cost
	was high as a result of the use of small circuit boards.  By
	packing a larger number of chips per board, similar function
	could be attained in a smaller volume because less interboard
	communication was required.  The PDP-8/E exploited this to achieve
	a new low in cost while attaining a new high in performance.

Reason for withdrawal:  This machine was slowly displaced by the PDP-8/A
	as the market for large PDP-8 configurations declined in the face
	of pressure from 16 bit mini and microcomputers.

Compatability:  As with the PDP-8/I and PDP-8/L, there are no limits on
	the combination of IAC and rotate instructions.  Unlike the early
	machines, basic Group 3 OPR operations for loading and storing
	the MQ register work even if there is no extended arithmetic
	element.  Finally, a new instruction was added, BSW; this swaps
	the left and right bytes in AC, and is encoded as a Group 1 OPR
	instruction using the "double the shift count bit".

	An odd quirk of this machine is that the RAL RAR combination ands
	the AC with the op-code, and the RTR RTL combination does an
	effective address computation loading the high 5 bits of AC with
	the current page and the lower bits of AC with the address field
	of the instruction itself!

	The EAE has a new mode, mode B.  Previous EAE designs were
	single-mode.  Mode B supports a large set of 24 bit operations
	and a somewhat more rational set of shift operations than the
	standard EAE.  All prior EAE designs would hang on the microcoded
	CLA NMI (clear/normalize) instruction applied to a nonzero AC.
	This instruction is redefined to be a mode changing instruction
	on the 8/E.

Standard configuration:  A CPU with 4K of memory, plus 110 baud current
	loop teletype interface.  Both a rack-mount table-top versions
	were sold (both 9" high by 19" wide by 21" deep).  The rack mount
	version was mounted on slides for easy maintenance.  The OMNIBUS
	backplane was on the bottom, with boards inserted from the top.

	The standard OMNIBUS backplane had 20 slots, with no fixed
	assignments, but the following conventional uses:

	-- KC8E programmer's console (lights and switches)
	-- M8300 \_ KK8E CPU registers
	-- M8310 /  KK8E CPU control
	--
	--
	-- M833  - Timing board (system clock)
	-- M865  - KL8E console terminal interface.
	--
	--
	--   -- space for more peripherals
	--
	--
	-- M849  - shield to isolate memory from CPU
	-- G104  \
	-- H220   > MM8E 4K memory
	-- G227  /
	--
	--   -- space for more memory
	--
	-- M8320 - KK8E Bus terminator

	Most of the early boards with 3 digit numbers were defective
	in one way or another, and the corrected boards added a trailing
	zero.  Thus, the M833 was generally replaced with an M8330, and
	the M865 was replaced with the M8650.

Expandability:  The following are among the OMNIBUS boards that could be
	added internally:

	-- M8650 - KL8E RS232 or current loop serial interface.
	-- M8340 \_ Extended arithmetic element.
	-- M8341 /  (must be attached in two slots adjacent to CPU.
	-- M8350 - KA8E posibus interface (excluding DMA transfers).
	-- M8360 - KD8E data break interface (one per DMA device).
	-- M837  - KM8E memory extension control (needed for over 4K).
	-- M840  - PC8E high speed paper tape reader-punch interface.
	-- M842  - XY8E X/Y plotter control.
	-- M843  - CR8E card reader interface.

	There were many other internal options.  There was room in the
	basic box for another 20 slot backplane; taking into account the
	2 slots occupied by the M935 bridge between the two backplanes,
	this allowed 38 slots, and a second box could be added to
	accomodate another 38 slot backplane, bridged to the first box by
	a pair of BC08H OMNIBUS extension cables.

	Given a M837 memory extension control, additional memory could be
	added in increments of 4K by adding G104, H220, G227 triplets.
	The suggested arrangement of boards on the OMNIBUS always
	maintained the M849 shield between memory other options.  The
	one exception was that the M8350 KA8E and M8360 KD8E external
	posibus interfaces were typically placed at the end of the
	OMNIBUS right before the terminator.

	The following options were introduced later, and there were many
	options offered by third party suppliers.

	-- G111  \
	-- H212   > MM8EJ 8K memory
	-- G233  /
	-- M8357 -- RX8E interface to RX01/02 8" diskette drives.
	-- M7104 \
	-- M7105  > RK8E RK05 Disk Interface
	-- M7106 /
	-- M8321 \
	-- M8322  \ TM8E Magtape control for 9 track tape.
	-- M8323  /
	-- M8327 /

	At one point, DEC packaged a PDP-8/E in a desk with no front panel
	controls other than power and bootstrap switch, along with an RX01
	accessable from the front and a VT50 on top.  This was sold as
	the Class-ic system, with an intended market in the classroom
	(hence the name); it was the forerunner, in terms of packaging,
	of many later DEC office products.

Survival:  It is still fairly common to find PDP-8/E systems on the
	surplus market, recently removed from service and in working
	condition or very close to it.  A modest number are no-doubt
	still in service, and there is still a limited amount of
	commercial support from both DEC and third-party vendors.

------------------------------

Subject: What is a PDP-8/F?

Date of introduction:  1972.
Date of withdrawal:    1978.

Technology:  an OMNIBUS machine, as with the PDP-8/E.  First use
	of a switching power supply in the PDP-8 family.

Reason for introduction:  The PDP-8/E had a large enough box and a large
	enough power supply to accomodate a large configuration.  By
	shortening the box and putting in a small switching power supply,
	a lower cost OMNIBUS machine was possible.

Reason for withdrawal:  The PDP-8/A 800 displaced this machine, providing
	similar expansion capability at a lower cost.

Compatability:  The PDP-8/F used the PDP-8/E CPU and peripherals.

Standard configuration:  Identical to the PDP-8/E, except that the KC8E
	front panel was replaced with a KC8M front panel that had LEDs
	instead of incandescent lights; this front panel could also be
	installed on PDP-8/E systems, but the PDP-8/E front panel could
	not be used on a PDP-8/F because of the lack of a +8 supply for
	the lights.  The original PDP-8/F box had a defective power
	supply, but a revised (slightly larger) box corrected this
	problem.

Expandability:  This machine could be expanded using all PDP-8/E OMNIBUS
	peripherals, including the external expansion chassis.  The
	relatively small internal power supply and the lack of room for
	a 20 slot bus expander inside the first box were the only
	limitations.  There were minor compatability problems with some
	options, for example, the power-fail auto-restart card, as
	originally sold, was incompatable with the PDP-8/F power supply.

Survival:  As with the PDP-8/E, these machines are moderately common on
	the surplus market, and frequently in working condition.

------------------------------

Subject: What is a PDP-8/M?

Date of introduction:  1972.
Date of withdrawal:    1978.

Technology:  This machine was a PDP-8/F (with a PDP-8/E CPU)

Reason for introduction:  DEC knew that OEM customers were an important
	market, so they packaged the PDP-8/F for this market, with no
	hardware changes behind the front panel.

Reason for withdrawal:  Same as the PDP-8/F

Compatability:  The PDP-8/M used the PDP-8/E CPU and peripherals.

Standard configuration:  Identical to the PDP-8/F, except that the KC8M
	front panel was replaced with a minimal function panel and the
	color scheme was different.  Because of this, one of the following
	options were required:

	-- M848  -- KP8E Power fail and auto-restart.
	-- M847  -- MI8E Hardware Bootstrap Loader.

	Expandability:  All options applying to the PDP-8/F applied.  In
	addition, the KC8M front panel (standard with the PDP-8/F) was
	available as an option.

Survival:  As with the PDP-8/F.

------------------------------

Subject: What is a PDP-8/A?

Date of introduction:  1975
Date of withdrawal:    1984
Also known as:
	DECdatasystem 310 (an 8/A 500 sold as a word-processor)

Technology:  This machine used the OMNIBUS with a new single-board CPU.
	The backplane was reoriented so that boards plugged into it from
	the front, with the board held horizontally.

Reason for introduction:  Using TTL MSI and LSI components, DEC was able
	to reduce the PDP-8 CPU to a single oversize board (formally, hex
	height, double width).  Similarly, they were able to make an 4K
	core memory board, and later, an 8K board in this format, and they
	were able to introduce a static RAM card using semiconductor
	memory.  The minimum system was reduced to 3 boards.

	The market for the PDP-8 was dominated by small systems, with
	fewer and fewer customers needing large-scale expandability.
	Thus, the 20 slot backplane of the early Omnibus machines was too
	big; with the new single board CPU and memory, a 12 slot backplane
	was enough, allowing further cost reductions.

Reason for withdrawal:  The market for the PDP-8 family was shrinking in
	the face of pressure from larger minicomputers and the new
	monolithic microcomputers.  After 1975, many PDP-8 sales were to
	captive customers who had sufficient software investments that
	they could not afford to move.  Only the word-processing and
	small business markets remained strong for first-time PDP-8
	sales, and in these, the specialized DEC VT-78 and DECmate
	machines were more cost effective than the open architecture
	OMNIBUS machines.
		
Compatability:  The new PDP-8/A CPU was largely compatable with the
	PDP-8/E CPU, except that the combination of RTR and RTL (Group 1
	OPR instructions) loaded the next address.  The power-fail
	auto-restart option included the standard skip on power low
	instruction, but also a new skip on battery empty instruction to
	test the battery used for back-up power on the new solid state
	memory.

	The standard parallel port on the M8316 port was not software
	compatable with the earlier line-printer interfaces used with
	device code 66.

Standard configuration:  The PDP-8/A was sold with a new short OMNIBUS
	backplane, mounted on its side above a power supply and a
	battery to back up the solid state memory.  The minimum
	configuration included a limited function control panel and the
	following components on the bus:

	-- M8315 -- KK8A CPU board
	-- M???? -- MS8A 1K to 4K solid state memory.
	-- M???? -- MR8A ROM companion for the MS8A.
	-- M8316 -- DKC8AA serial/parallel interface and clock.

	The M8316 board contained a remarkable but useful hodgepodge of
	commonly used peripherals, including the console terminal
	interface, a parallel port, the power/fail auto-restart logic,
	and a 100 Hz real time clock.

	The original configuration sold had a 10 slot backplane and a
	poor power supply.  The later base model had a 12 slot backplane,
	the 8/A 400.

Expandability:  All PDP-8/E peripherals and options could be used with
	the PDP-8/A.  The KK8A cpu was not as fast as the KK8E used in
	the PDP-8/E, but the KK8E CPU could be substituted for the KK8A
	CPU, and many PDP-8/A systems were sold with this substitution.

	A box with a 20 slot backplane, the 8/A 600, was available for
	large configurations.  A pair of PDP-8/A backplanes could be
	connected using BC08H cables, and there was a special cable,
	the BC80C, for connecting a hex wide 8A backplane to a PDP-8/E,
	-8/F or -8/M backplane.

	By late 1975, the PDP-8/A was being sold in a workstation
	configuration, with the CPU and dual 8" diskette drives in a desk
	with a video terminal (VT52) and letter quality printer on top.
	This followed the pattern set by the Class-ic packaging of the
	PDP-8/E, but it was aimed at the word-processing market.

	The following additional PDP-8/A (hex) boards were offered:

	-- G649  \_ MM8AA 8K Core stack (too slow for 8/E CPU!).
	-- H219A /  MM8AA 8K Core memory control.
	-- G650  \_ MM8AB 16K Core stack (ok for 8/E CPU!).
	-- H219B /  MM8AB 16K Core memory control.
	-- M???? -- MR8F 1K ROM (overlayable with core).
	-- M8317 -- KM8A memory extender (with variations).
	-- M8319 -- KL8A 4 channel RS232 or current loop serial I/O.
	-- M8433 -- RL8A controller for 1 to 4 RL01/RL02 disk drives.
	-- M???? -- FPP8A floating point processor.

	The PDP-8/A model 800 was the same as the model 600, but with the
	FPP8A floating point processor included as part of the package.

	-- M8416 -- KT8AA Memory management unit for up to 128K.
	--       -- KC8AA Programmer's Console (requires M8316)
	-- M8417 -- MSC8DJ 128K DRAM MOS Memory.

	Note that memory extension to 128K was a new PDP-8/A feature that
	was necessarily incompatable with the older PDP-8 memory expansion
	options, although the conventional PDP-8 memory expansion
	instructions still operate correctly on the first 32K.  Access to
	additional fields involved borrowing IOT instructions that were
	previously dedicated to other devices.

	The MM8A options require the use of a box with a -20V power supply.
	Also, the use of the MSC8 DRAM memory cards requires a CPU that
	supports the memory stall signal, early PDP-8/E CPUs did not.

Survival:  As with the PDP-8/E, these machines are moderately common on the
	surplus market and a modest number are still in use.  Because the
	original machines were less expensive than and slower than 8/E,
	they are more likely to be simply discarded instead of sold as
	surplus.

------------------------------

Subject: What is a VT78?

Date of introduction:  1978
Date of withdrawal:    1980 (Displaced by the DECmate)
Also known as:  DECstation 78 

Technology:  Based on the Intersil/Harris 6100 microprocessor, packaged
	in a VT52 case.  The 6100 processor was able to run at 4 MHz, but
	in the VT78, it was only clocked at 2.2 MHz because of the speed
	of the DRAM used and the deliberate use of graded out chips.

Reason for introduction:  Using TTL MSI and LSI components, DEC could
	pack a system into vacant space in a standard terminal case,
	allowing PDP-8 systems to compete with personal computers in the
	small business and office automation market.  This was a natural
	follow-on to the desk-mounted workstation configurations in which
	the PDP-8/A was already being sold.

Compatability:  The Group I OPR combinations RAL RAR and RTL RTR are
	no-ops.  Unlike all earlier PDP-8 models, autoindex locations
	10 to 17 (octal) only work in page zero mode; these operate like
	all other memory locations when addressed in current page mode
	from code running on page zero.  Other than this, it is fully
	PDP-8/E compatable, even at the level of I/O instructions for
	the standard periperals; this was the last PDP-8 to offer this
	level of compatability.

	It was not possible to continue from a halt without restarting
	the machine.  In addition, none of the peripherals available on
	this machine needed DMA (data break) transfers.

Standard configuration:  The VT78 was sold with 16k words of DRAM with
	the keyboard and display of the VT52 terminal.  An RX01 dual 8"
	diskette drive was standard, packaged in the pedestal under the
	terminal.  The console (device 03/04) and the serial ports
	(devices 30/31 and 32/33) are compatible with the M8650 KL8E,
	with the latter extended to allow software controlled baud rate
	selection.  There are two parallel ports; device 66 (compatible
	with the M8365 printer controller) and device 47, compatible with
	the nonstandard port on the M8316 DKC8AA.  There is also a 100Hz
	clock compatible with the clock on the M8316 DKC8AA.

	The standard ROM boots the system from the RX01 after setting the
	baud rates to match that selected by the switches on the bottom
	of the VT52 case.

Expandability:  This was a closed system, with few options.  The base
	configuration was able to support two RX01 drives (later RX02),
	for a total of 4 transports.  Various boot ROM's were available,
	including a paper-tape RIM loader ROM for loading diagnostics
	from tape.  Another ROM boots the system from a PDP-11 server in
	the client/server configuration used by WPS-11.

Survival:  There are probably many VT78 systems still in use.

------------------------------

Subject: What is a DECmate I?

Date of introduction:  1980
Date of withdrawal:    1984 (Phased out in favor of the DECmate II)
Also known as:  DECmate (prior to the DECmate II, no suffix was used)
		VT278

Technology:  Based on the Intersil/Harris 6120 microprocessor,
	packaged in a VT-100 box with keyboard and display.

Reason for introduction:  This machine was aimed primarily at the market
	originally opened by the VT78, using the IM6120 as a substitute
	for the older 6100 chip and optimizing for minimum cost and mass
	production efficiency.

Compatability:  A new feature was introduced in the 6120 microprocessor:
	The Group I OPR combination RAL RAR was defined as R3L, or rotate
	accumulator 3 places left, so that byte swap (BSW) is equivalent
	to R3L;R3L.  RTR RTL remained a no-op, as in the 6100.

	Also, the EAE operations not implemented in the basic CPU cause
	the CPU to hang awaiting completion of the operation by a
	coprocessor.  Unfortunately, no EAE coprocessor was ever offered.

	The printer port offered software baud-rate selection compatable
	with the VT78 baud-rate selection scheme.  The dual-port data
	communications option was flexible but completely incompatable
	with all previous PDP-8 serial ports.

	The console and printer ports are not fully compatable with the
	earlier PDP-8 serial ports.  Specifically, on earlier serial
	interfaces, it was possible to test flags without resetting them,
	but on the DECmate machines, testing the keyboard input flag
	always resets the flag as a side effect.  In addition, on the
	console port, every successful test of the flag must be followed
	by reading a character or the flag will never be set again.

	It was not possible to continue from a halt without restarting
	the machine.

	The large amount of device emulation performed by the CPU in
	supporting screen updates severely limits the ability of the
	system to run in real time.

Standard configuration:  The DECmate I was sold with 32k words of memory,
	with a small control memory added to handle control/status,
	console device emulation and boot options.  The console terminal
	keyboard and display functions are largely supported by code
	running in control memory (a less expensive alternative to
	dedicating hardware for this, as was done in the VT78).

	The DECmate I came with an integral printer port, compatable with
	the VT78 (device 32/33), and it had an RX02 dual 8 inch diskette
	drive, mounted in the short pedistal under the terminal/CPU box.
	A 100Hz clock was included, as in the VT78 and PDP-8/A.

Expandability:  This was a closed system, with limited options.
	Specifically, a second RX02 could be connected (or an RX01,
	because that had a compatable connector), the DP278A and DP278B
	communications boards (really the same board, but the DP278B had
	2 extra chips), and the RL-278 disk controller, able to accomodate
	from 1 to 4 RL02 rack mount disk drives.

	When the DP278A option is added, additional routines in control
	memory come alive to handle terminal emulaton and allow diskless
	operation.  The terminal emulator is an extended VT100 subset
	that is essentially compatable in 80 column mode.  The DP278A
	option could support both asynchronous and synchronous protocols,
	and the DP278B could handle SDLC and other nasty bit-stuffing
	protocols.

	Various pedestal and desk configurations were sold for housing
	the RX01 and RX02 drives, most being teacart style designs, but
	there was also a pedestal version that was essentially a
	repackaging of the RX02 with either 2 or 4 new 8 inch disk
	transports (physically incompatable with earlier DEC transports).

Survival:  Many DECmates are still in use, and they are fairly common on
	the surplus market.  They are found in small numbers just about
	anywhere large numbers of early PC vintage machines are found.

------------------------------

Subject: What is a DECmate II?

Date of introduction:  1982
Date of withdrawal:    1986 
Price: $1,435

Technology:  Based on the 6120 microprocessor, this shared the same
	packaging as DEC's other competitors in the PC market, the
	Rainbow (8088 based) and the PRO-325 (PDP-11 based).

Reason for introduction:  This machine was introduced in order to allow
	more flexibility than the DECmate I and to allow more sharing of
	parts with the VT220 and DEC's other personal computers.

Compatability:  Same as the DECmate I, except it could continue from a
	halt.  There was better hardware for device emulation support,
	allowing for somewhat better real-time performance.  The data
	communications port was an incompatable improvement on the
	incompatable DECmate I communications port.  No built-in terminal
	emulation was provided, and the data communications port supported
	only one line, but aside from this, the data communications port
	is essentially as powerful as the DP-278B on the DECmate I.

Standard Configuration:  The DECmate II was sold with 32K of program
	memory, plus a second full bank for dedicated control panel
	function emulation.  Code running in the second bank is sometimes
	referred to as slushware; it looks like hardware to the PDP-8
	user, but it is actually device emulation software that is loaded
	from the boot diskette.

	An integral RX50 dual 5 1/4 inch diskette drive with an 8051
	controller chip was included, along with a printer port, a 100Hz
	real-time clock, single data communications port, and interfaces
	to the monitor and keyboard.  The diskette drive can read
	single-sided 48 track-per-inch diskettes, so it might be possible
	to read (but not write) IBM PC diskettes on it.

Expandability:  This was the most open of the DECmate systems, with a
	number of disk options:  An additional pair of RX50 drives could
	be added, and with the RX78 board, it could support a pair of
	dual 8 inch drives, either RX01 or RX02.

	As an alternative to the RX78, there was a controller for an
	MFM hard drive.  The interface to the RX78 board wasn't fully
	compatable with earlier interfaces to RX01 and RX02, and there
	was no way to have both an RX78 and an MFM drive.  The MFM drive
	could be up to 64 MB, with 16 sectors per track, 512 bytes each
	and at most 8 heads and 1024 (or possibly 4096) cylinders.  A
	power supply upgrade was needed to support the MFM drive.  DEC
	sold this machine with 5, 10 and 20 meg hard drives, Seagate
	ST-506, 412, and 225 respectively.

	A graphics board supporting a color monitor could be added in
	addition to the monochrome console display; two variants of
	this board were produced during the production run, all slightly
	incompatable.

	A coprocessor board could be added, with communication to and
	from the coprocessor through device 14.  DEC sold three boards,
	an APU board (Z80 and 64K), and two XPU boards (Z80, 8086 and
	either 256K or 512K).  If these added processors are used, the
	6120 processor is usually used as an I/O server for whatever
	ran on the coprocessor.  The XPU boards used a Z80 for I/O
	support, so 8086 I/O was very indirect, particularly if it
	involved I/O to a PDP-8 device that was emulated from control
	memory.  Despite this, the DECmate version of MS/DOS is generally
	faster than MS/DOS on more recent 80286 and 80386 based IBM PCs
	because of effective use of the coprocessors (but they couldn't
	run MS/DOS code that bypasses MS/DOS for I/O).

Survival:  As with the DECmate I.

------------------------------

Subject: What is a DECmate III?

Date of introduction:  1984
Date of withdrawal:    1990 
Price: $2,695

Technology:  Same as the DECmate II.

Reason for introduction:  Again, DEC discovered that the market for large
	systems was dominated by other products, and that the PDP-8 based
	products were rarely expanded to their full potential.  Thus,
	there was no point in paying the price for expandability.

Compatability:  Same as the DECmate II, except that the printer port is
	fixed at 4800 baud.

Standard Configuration:  The DECmate III was sold with 32K of program
	memory, plus a second full bank for dedicated control panel
	functions, an integral RX50 dual 5 1/4 inch diskette drive with
	an 8051 controller chip, a printer port, a 100Hz real-time-clock,
	a data communications port, and interfaces for the VR-201 monitor
	and keyboard.

Expandability:  A revised version of the Z80 based coprocessor for the
	DECmate II was available, and a graphics board largely compatable
	with the later DECmate II graphics board could be added allowing
	the standard monochrome monitor to be replaced with a VR-241 color
	monitor.  Two monitor configurations were not supported.  An
	obscure variant of the DEC scholar modem was also supported as
	an option.

Survival:  As with the DECmate I.

------------------------------

Subject: What is a DECmate III+?

Date of introduction:  1985
Date of withdrawal:    1990 

Technology:  Same as the DECmate II.

Reason for introduction:  This machine apparently represents the last
	gasp of the PDP-8, hunting for the remains of the ever-shrinking
	market niche that the earlier DECmates had carved out.  The
	market niche was not there, and the production runs for this
	machine were short enough that UV erasable EPROM technology was
	used where earlier DECmates had used mask programmed chips.

Compatability:  Same as the DECmate II, but the machine was unable to
	read 48 track per inch IBM formatted diskettes.  Again the
	printer port was fixed at 4800 baud.

Standard Configuration:  The DECmate III+ was sold with 32K of program
	memory, plus a second bank for dedicated control panel functions,
	an integral RX33 single 5 1/4 inch diskette drive with an 8751
	controller chip, a printer port, a data communications port and
	interfaces to the monitor and keyboard.  A hard disk controller
	compatable with the optional one on the DECmate II was included,
	supporting an integral ST-225 20 MB disk; it is likely that it
	can only handle up to 1024 cylinders, but it is otherwise
	compatable with the DECmate II.

Expandability: The same coprocessor option sold with the DECmate III was
	available, but because of the difficulty of adding a second floppy
	drive, this was rarely used (the Z80 was most likely to be used
	to run CP/M, but that system requires two drives to handle the
	installation procedure; an appropriately configured bootable
	image created on a DECmate II or III could run on a DECmate III+).

	The same graphics board as used on the DECmate III was also
	available.  The circuit traces and connectors for the Scholar
	modem are present, but this option was never sold on the
	DECmate III+.

Survival:  As with the other DECmates.

------------------------------

End of PDP-8 Summary of Models and Options (posted every other month)
*********************************************************************

Article 1117 of alt.sys.pdp8:
Newsgroups: alt.sys.pdp8
Path: bigblue.oit.unc.edu!concert!news-server.ncren.net!taco.cc.ncsu.edu!lll-winken.llnl.gov!uwm.edu!math.ohio-state.edu!howland.reston.ans.net!Germany.EU.net!news.dfn.de!news.rwth-aachen.de!urmel.informatik.rwth-aachen.de!newsserver.rrzn.uni-hannover.de!news
From: [email-masked] (Bernhard Baehr)
Subject: Macintosh PDP-8/E Simulator
Message-ID: <[email-masked]>
Sender: [email-masked] (News Service)
Reply-To: [email-masked]
Organization: RRZN
Date: Fri, 9 Dec 1994 16:25:50 GMT
Lines: 40

I announce the availability of the beta version of my simulator for 
the DEC PDP-8/E minicomputer running on the Apple Macintosh computer.
The simulated machine is a PDP-8/E with 4K words of memory and a 
ASR 33 console teletype. Optionally a MC8-E Memory Extension (with 
up to 32K words of memory), an EAE, an auxiliary ASR 33 teletype, a 
high speed paper tape reader and punch, a RK8-E disk system, a 
LP8-E line printer and a Real Time Clock can be attached to the 
simulated PDP-8/E.

The simulator is based on the PDP-8/E emulator of Bill Haygood. It
is known to run on a wide variety of Macintosh computers from the
SE/30 to the Power Macintosh running System 6.0.4 to 7.5. (Probably
it runs on any Macintosh with System 4.1 or better and 128K ROMs.)
On the fastest 68040 Macintoshs the simulated PDP-8/E runs nearly 
with the speed of a hardware PDP-8/E.

The simulator provides a comfortable user interface for running,
writing and debugging PDP-8 software. For each device, there is a
separate window which displays the internal state of the device
(e. g. register and - disassembled - memory content). Register and
memory content can be modified by mouse clicking. Other features of
the simulator are breakpoints, break opcodes, single step execution,
a trace mode for the PDP-8/E and much more. The simulated ASR 33 
teletypes provide all comfort of Macintosh text editor windows. 

There is no manual for the PDP-8/E Simulator, but the program has
full Balloon Help support, and there is a help window which gives
detailed information about the PDP-8 instruction set implemented by
the simulator and hints for operating the simulator.

Anybody who wants to use and test the simulator, which, although it 
is version 1.0 beta, has reached a very stable state, may ask me to
send him a copy of the program by E-mail.

Bernhard Baehr
[email-masked]

Article 1118 of alt.sys.pdp8:
Newsgroups: alt.sys.pdp8
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From: [email-masked] (Ed Moran)
Subject: Historical clubs, newsletters?
Message-ID: <[email-masked]>
Organization: NETCOM On-line Communication Services (408 261-4700 guest)
X-Newsreader: TIN [version 1.2 PL1]
Date: Sat, 10 Dec 1994 17:14:22 GMT
Lines: 24

Hi, all!
 
   I'm getting used to my internet account now.

   I was wondering..  Are there any organizations around for old computer
buffs?  Informal clubs and newsletters?  I've discovered the IEEE's Annals
of computer history, and found a fair number of books on the subject (thank
you, Mr Cortada, wherever you are..)  But I'm looking for a way to find old
machines (I have a garage now, too ..=]), and hopefully have a shoulder to
cry on when I try to get it running.
 
   As for myself, I worked a couple of summers at the old Byte Shop on
Bascom, San Jose, building Imsais and fixing Altairs, and always had a
passing interest in restoring a PDP-11, a Nova or the like.  Now that I have
the resources, I'm beginning the search.  Any ideas?  Where do mainframes
go whenthey die?

   Thanks!
 
  - Ed

-- 
Ed Moran, [email-masked]   The above opinions are unsuitable for re-use,
PO Box 72OO72  San Jose, Calif.         Please dispose of properly.

Article 1119 of alt.sys.pdp8:
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From: [email-masked] (Harris Newman)
Newsgroups: alt.sys.pdp8
Subject: PDP-10 Emulator wanted
Date: 10 Dec 1994 00:05:54 GMT
Organization: Real/Time Communications - Bob Gustwick and Associates
Lines: 8
Message-ID: <[email-masked]>
NNTP-Posting-Host: ivy.bga.com
X-Newsreader: TIN [version 1.2 PL2]

Sorry bout the misspost, but yall may know of a pdp-10 emulator out there.

--
Remember:
Zero is always better than nothing!
[email-masked]

Article 1120 of alt.sys.pdp8:
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From: [email-masked] (Douglas W. Jones,201H MLH,3193350740,3193382879)
Newsgroups: alt.sys.pdp8
Subject: Re: Historical clubs, newsletters?
Date: 12 Dec 1994 17:11:52 GMT
Organization: University of Iowa, Iowa City, IA, USA
Lines: 66
Distribution: world
Message-ID: <[email-masked]>
References: <[email-masked]>
NNTP-Posting-Host: pyrite.cs.uiowa.edu

From article <[email-masked]>,
by [email-masked] (Ed Moran):
> 
>    I was wondering..  Are there any organizations around for old computer
> buffs?
>
> Ed Moran, [email-masked]
> PO Box 72OO72  San Jose, Calif.

You want to get in touch with the Computer History Association of
California.  Here are some snips from the most recent edition of their
newsletter:

          -------------------------------------------------
                      The ANALYTICAL ENGINE
     Newsletter of the Computer History Association of California
                         ISSN 1071-6351

     Volume 2, Number 2, October 1994
     Kip Crosby, Managing Editor
     Jude Thilman, Telecommunications Editor
          -------------------------------------------------

     Computer History Association of California
     3375 Alma Street
     Apt. 263
     Palo Alto, CA 94306-3518

     -------------------------------------------------
     ADDRESSES OF CORRESPONDING ORGANIZATIONS
     -------------------------------------------------

     Charles Babbage Institute, 103 Walter Library, 117 Pleasant 
     Street SE, Minneapolis, MN 55455. Judy E. O'Neill, associate 
     director.

     The Computer Museum, 300 Congress Street, Boston MA 02210. Brian 
     C. Wallace, curator of historical computing.

     Historical Computer Society, 10928 Ted Williams Place, El Paso 
     TX 79934. CompuServe 100116,217. David A. Greelish, director and 
     editor.  ------ this address is out of date --------

     International Association of Calculator Collectors, 10445 
     Victoria Avenue, Riverside CA 92503. Guy Ball, Bruce L. Flamm, 
     directors.

     International Interactive Communications Society, 2601 Mariposa 
     Street, San Francisco CA 94110. Sheila Farrell, membership 
     secretary.

     Lambda Software Publishing, 149 West Hilliard Lane, Eugene OR 
     97404. David A. J. McGlone, editor and publisher.

     _The Mathematical Intelligencer_, Springer-Verlag New York, 175 
     Fifth Avenue, New York, NY 10010. Chandler Davis, editor-in-
     chief.

     Unusual Systems, 220 Samuel Street, Kitchener, Ontario N2H 1R6, 
     Canada. Kevin Stumpf, president.

Hope all that helps!

				Doug Jones
				[email-masked]

Article 1121 of alt.sys.pdp8:
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From: [email-masked] (George Bray)
Newsgroups: decus.nop,aus.general,aus.comms,alt.sys.pdp8,alt.sys.pdp11,biz.dec
Subject: Re: Aust. COMPUTER MUSEUM Society now Official.
Date: Thu, 22 Dec 1994 23:55:49 +1000
Organization: Sand Consulting Pty Ltd
Lines: 16
Message-ID: <[email-masked]>
References: <[email-masked]>
NNTP-Posting-Host: dialup-17.mpx.com.au
Xref: bigblue.oit.unc.edu alt.sys.pdp8:1121 biz.dec:654

> 
> Current membership fees are     $25.oo for individuals
>                                 $10.oo for students/pensioners
> 
> Membership forms are available from the Secretary or Treasurer.

Are the forms on the web?

> 
> 
> v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v
>  John Geremin, Treasurer, Australian COMPUTER MUSEUM Society Inc. 
> -^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-

George Bray

Article 1122 of alt.sys.pdp8:
Newsgroups: alt.sys.pdp8
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From: [email-masked] ("Stephen Walters")
Subject: Re: Historical clubs, newsletters?
Message-ID: <[email-masked]>
Organization: Skills Unlimited              
References: <[email-masked]>
Date: Wed, 21 Dec 1994 21:54:18 GMT
X-News-Software: Ameol
Lines: 19

Well in London, there is the 

CLASSIC COMPUTER CLUB

Setup, by ME, to help people who are interested in collecting old 
computers. My oldest machine is my 12kword PDP 8e with duff asr33, 
Intersil Intercept, and very shortly a Valve Analog Computer (age unknown 
and VERY big).

My tel no is +44 0956-544202 Mercury 1-2-1 mobile
and I have e-mail and on occasion FAX, too.

The club has been running for ? five years and is quite small group. 
Every time we get publicity the is a barrage of e-mails, snail-mail 
'phone calls etc.

I just thought I'd mention it.

[email-masked]

Article 1123 of alt.sys.pdp8:
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Newsgroups: decus.nop,aus.general,aus.comms,alt.sys.pdp8,alt.sys.pdp11,biz.dec
Subject: Aust. COMPUTER MUSEUM Society now Official.
Message-ID: <[email-masked]>
From: [email-masked]
Date: 21 Dec 94 22:35:01 AEST
Organization: DECUS Australia
Lines: 57
Xref: bigblue.oit.unc.edu alt.sys.pdp8:1123 biz.dec:655

						<news_release.941221>

		AUSTRALIAN  COMPUTER  MUSEUM  SOCIETY
		NOW INCORPORATED in NEW SOUTH WALES.

The Australian Computer Museum Society is now incorporated as from the
16th December, 1994 under the Associations Incorporation Act 1984 (in NSW).

The President is	Graeme PHILIPSON,	phone	02-286 5900,
						fax	02-267 2094,

				e-mail  IN%"[email-masked]"

The Secretary is	Michael CHEVALLIER,	phone   02-498 3383,

				e-mail	IN%"[email-masked]"

The Treasurer is	John GEREMIN,		phone   02-764 4855,
						fax	02-764 4679,

				e-mail	IN%"[email-masked]"

The society's ADDRESS is

	Australian COMPUTER MUSEUM Society Inc.
	c/-  P.O. Box 103,  Killara, NSW, 2071.  Australia.

	____________________________________________________

The Society is seeking BUSINESS SPONSORSHIPS from Computer Businesses
to help pay the rent on its storage space at Homebush.

In the new year the society will be looking for VENDOR SPONSORSHIPS 
from Computer Manufacturers to employ part-time curators.

The Society also needs COMMERCIAL SPONSORS and DONATIONS from any 
interested business to help us establish our offices and to institute
our special projects.

	____________________________________________________

Current membership fees are	$25.oo for individuals
				$10.oo for students/pensioners

Membership forms are available from the Secretary or Treasurer.

v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v
 John Geremin, Treasurer, Australian COMPUTER MUSEUM Society Inc. 
-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-

Article 1124 of alt.sys.pdp8:
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From: [email-masked]
Newsgroups: decus.nop,aus.general,aus.comms,alt.sys.pdp8,alt.sys.pdp11,biz.dec
Subject: Re: Aust. COMPUTER MUSEUM Society * Mship Form.
Message-ID: <[email-masked]>
Date: 23 Dec 94 23:14:46 AEST
References: <[email-masked]> <[email-masked]>
Organization: DECUS Australia
Lines: 91
Xref: bigblue.oit.unc.edu alt.sys.pdp8:1124 biz.dec:656

In article <[email-masked]>, [email-masked] (George Bray) writes:
>> 
>> Current membership fees are     $25.oo for individuals
>>                                 $10.oo for students/pensioners
>> 
>> Membership forms are available from the Secretary or Treasurer.
> 
> 
> Are the forms on the web?

	Not really - but one is appended here. 
>> 
>> 
>> v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v
>>  John Geremin, Treasurer, Australian COMPUTER MUSEUM Society Inc. 
>> -^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-
> 
> George Bray
-- 

Regards,   John G.		(alias 'megaJOHN')
v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v
 John Geremin, Treasurer, Australian COMPUTER MUSEUM Society Inc. 
IN%"[email-masked]"   or  fax: 02- 764 4679  (24 hours).
-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-^-

---<cut here>----

Application for Membership of Society.

          Australian COMPUTER MUSEUM Society Inc.   
          =======================================

I, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
               (full name of applicant)

of . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
               (residential address)

. . . . . . . . . . . . . . . . . . . .  hereby apply to become a member 
               (occupation)                  
of the Australian Computer Museum Society Inc. In the event of my admission
as a member, I agree to be bound by the rules of the society for the
time being in force.

 . . . . . . . . . . . . . . . . . . . . . . . .   Date . . / . . . / . .
           Signature of applicant 

Phone (Home). . .- . . .  . . . .  E-mail . . . . . . . . . . . . . . . . .

Phone (Bus.). . .- . . .  . . . .  Fax . . . . . . . Mobile . . . . . . . .

Postal Address  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Membership Fees      $  25.oo per annum.   [$10.oo pensioner/student]

Business Sponsorships are welcome, please call the Treasurer, 02-764 4855.

return form, cheque to:  A.C.M.S.Inc.  p.o. box 103,  KILLARA.  NSW  2071.
                         ------------  -------------  --------------------

               A. C. M. S.  Initial  Member  Survey.

Please tick below your special interests in A.C.M.S. project activities,

a)  . . .  Computer Hardware - collection and restoration.

b)  . . .  Software Archive and Media Repository.

c)  . . .  Oral History - Interviews and followups.

d)  . . .  Library of Manuals and other printed documentation.

e)  . . .  Database of Technical - Personal - General Information.

f)  . . .  Committee assistance - general organisation.

g)   other special interests . . . . . . . . . . . . . . . . . . . . . . .

     . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

h)   personal collection . . . . . . . . . . . . . . . . . . . . . . . . .

     . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

     . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

     . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

-----<end>-----