Subject: Re: New owner of a PDP-8e

From: [email-masked] (Douglas W. Jones,201H MLH,3193350740,3193382879)
Date: Tue, 27 Oct 1992 19:45:07 GMT

>From article <[email-masked]>,
by [email-masked] (CP/M lives!):
> In article <[email-masked]>,
> [email-masked] (Erkki Ruohtula) writes:
>> A strange word size. How do you normally process characters on this box?
> 
> The primary choices are 6-bit characters (this is 1963, after all) or
> 7-bit characters with the 8th bit set to one and the remaining bits 
> unused.

Well, he said an 8/e, and that was 1969.  The end of the line for the
PDP-8 family was in 1990, with the DECmate III+, which is well into the
ASCII era.

>From the start, all PDP-8 files have been stored as 8 bit ASCII, which is
to say, 7 bit ASCII with the high bit set to one.  The reason is that
these machines were used, from the start, with teletypes (preferably
model ASR-33) which used a 64 character subset of this code (upper case
only).  Initially, most software development was done with punched paper
tape, so it was natural to process one character per 12 bit word.

Error messages and other text constants that were embedded in programs
were frequently stored in a compact 6 bit character set, with special
routines to unpack the codes.

When ASCII is packed into 12 bit words, triplets of ASCII characters are
packed into pairs of words, two successive characters in the two
successive words, right justified, and the third character split into
two nibbles and stored left justified in the remaining nibbles of both
words.

I have 1964 through 1966 vintage source listing of large amounts of PDP-8
system software (such as the FORTRAN compiler and both the PAL and MACRO-8
assemblers), and these very clearly document the standards used for text
processing back then on this family of machines.
> 
> Anyone planning a big bash for the PDP-5's 30th birthday?

No, but someone ought to do so!  Who's got a working PDP-5 to use as the
centerpiece of the celebration?  DEC ought to be willing to help with the
price of beer and publicity.
				Doug Jones
				[email-masked]

---

From: [email-masked] (Jeff Russ)
Date: Wed, 28 Oct 1992 04:32:36 GMT

>price of beer and publicity.

I've got an intact PDP-5 but no schematics or manuals.  If anyone has
any leads who might have some please let me know.  I'll pay in cash or
beer.

----------------------------------------------------------------------------
Jeff Russ				[email-masked]
University Computing Services		PHONE: (812) 855-2733
Indiana University, Bloomington, IN     I want to buy old PDP[4-9] systems.

---

From: [email-masked] (Charles Lasner)
Date: Wed, 28 Oct 1992 05:52:05 GMT

>PDP-8 family was in 1990, with the DECmate III+, which is well into the

Earliest 8/e prototype I am aware of is late 1970.

>tape, so it was natural to process one character per 12 bit word.

Let's make that a little clearer:

OS/8 was started in 1970, and that's the way *it* does it!  In essence,
mistrust and strip out the high-order bit, since you can't trust what the
terminals might set the bit to.  Teletypes generally set it, but other devices
might vary, such as VT05 terminals introduced slightly earlier.

Before that was the Disk Monitor, whose ASCII format was the case-shift
method using 6-bit upper-case code and a transient case-control character
for the (presumedly) infrequent occurence of lower-case.

There are other systems, but this is what DEC supported.

>routines to unpack the codes.

These are the programmer's methods of storing strings within his
programs loaded into 12-bit memory, not the O/S's method of storing the
source files.  The six-bit code could either be "straight" and upper-case
only, or with a locking or transient case-shifter as required.  Also,
some codes can be reserved for other functions such as imbedded CR/LF
impliers, etc.  This allows multi-line messages at the expense of the
loss of certain reserved characters.

The P?S/8 upper-case file structure uses 6-bit storage, with the "_" character
removed and instead it implies <HT> (^I).  The "@" char is also disallowed
and is used for both EOL and EOF.  (It serves both purposes by using a trick
of "alignment".)  P?S/8 is a proprietary alternate O/S for the -8's and
DECmates, and is not a DEC product.

>two nibbles and stored left justified in the remaining nibbles of both

This is known as "3 for 2" and is quite commonly used.  Even binary 
paper-tape-frame files use this format, except that each 8-bit char now
uses all 8 bits, while ASCII text only uses the low-order 7 bits of each
8 bits.

>price of beer and publicity.

I once worked on a -5, but I don't have one, but I do have a few Systems
Modules such as were used in it :-).

cjl

---

From: [email-masked] (Jordin Kare)
Date: Wed, 28 Oct 1992 23:52:58 GMT

>price of beer and publicity.

Migawd!  30 years of PDP-5's!  You might check with the MIT Electronics
Research Society, room 20B119 (?) at MIT.  They used to have a PDP-5
(I know because I rebuilt it, long ago in my college days) and may
well either still have it or know where it went.  Geoff Rochat would
be the person to ask.

	Jordin Kare
-- 

	Jordin Kare	[email-masked]	510-426-0363

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From: [email-masked] (Paul Pierce)
Date: Fri, 30 Oct 1992 21:56:16 GMT

In article <[email-masked]>, [email-masked] (Douglas W. Jones,201H MLH,3193350740,3193382879) writes:
|> From article <[email-masked]>,
|> by [email-masked] (CP/M lives!):
|> > 
|> > Anyone planning a big bash for the PDP-5's 30th birthday?
|> 
|> No, but someone ought to do so!  Who's got a working PDP-5 to use as the
|> centerpiece of the celebration?

The Computer Museum has one, I don't know if it works.
I have one which needs a lot of work. Someone modified it to have a real PC!
[cf. previous thread about PDP-5 front panels]

-- 
Paul Pierce			[email-masked]
Intel