Subject: Re: The Analytical Engine (CHAC newsletter!)

From: [email-masked] (Adam Justin Thornton)
Date: 2 Sep 93 23:33:23 GMT

In article <[email-masked]> jones@pyrite (Douglas W. Jones,201H MLH,3193350740,3193382879) writes:

>2) Pong was not a computer game!  It was a video game implemented with
>   TTL logic, with no computer.

Hey.  Enough TTL _is_ a computer.  Just 'cause it didn't have an LSI
CPU...sheesh.  I think I still have my old home version of _Super Pong_ (4
whole games!); I wonder if I clean the crud from the battery case if it'll
still work.

Adam
-- 
[email-masked] | These?  Rice's opinions?  Yeah, right.  |  "Might there have
been fewer crimes in the name of Jesus, and more mercy in the name of Judas
Iscariot?"--Thomas Pynchon | Overheard in Waco: "This is not an assault."
Save the Choad! | Win/NT: Yesterday's technology tomorrow. | 64,928 | Fnord

---

From: jones@pyrite (Douglas W. Jones,201H MLH,3193350740,3193382879)
Date: Fri, 3 Sep 1993 14:09:27 GMT

>From article <[email-masked]>,
by [email-masked] (Adam Justin Thornton):

> In article <[email-masked]>
> jones@pyrite (Douglas W. Jones,201H MLH,3193350740,3193382879) writes:
> 
> CPU...sheesh.

And I collect computers made with TTL without an LSI CPU; I have three
of them sitting in my study right now at home!  Still, Pong isn't a
computer game because it doesn't have a computer!  I'm using the standard
definition of a computer -- that is, a general purpose machine capable
of executing a program provided by the user.  The logic inside a Pong
game is a special purpose controller with a single fixed (but fairly
complex) program that does only one thing.

The border between computers, calculators and controllers can get fuzzy,
for example, ENIAC was clearly a programmable calculator, but was it a
computer?  You could reprogram it with a patch panel change, and it was
powerful enough that someone could have programmed a patch panel to make
it interpret a stored program, but to my knowledge, nobody did it.

You can't make that kind of quibble about Pong though.  There were no
provisions for even rudimentary programmability.

				Doug Jones
				[email-masked]

---

From: [email-masked] (David Hembrow)
Date: Fri, 3 Sep 1993 15:53:49 GMT

>it interpret a stored program, but to my knowledge, nobody did it.

Not a quibble, but possibly the start of a new interesting thread:

Is this in fact true ? If you know enough about the way in which ENIAC
was put together, could you provide some details of what it was in fact
capable of ? I'd be interested in knowing something about the workings
of some of these early computers ( especially the programmable ones ).

ie.

o Amount of memory
o Instruction set
o I/O capabilities

I'm afraid there isn't a lot I can contribute to this, I know only
what I've read in various books. They tend to give information like
the number of valves ( tubes ) in each machine and make some statement
about the number of operations a second it was apparently capable of
but little more.

David.

---

From: [email-masked] (Douglas W. Jones)
Date: Fri, 3 Sep 1993 18:56:32 GMT

>From article <[email-masked]>,
by [email-masked] (David Hembrow):
>
> I'd be interested in knowing something about the workings
> of some of these early computers

That's why I prepared the alt.sys.pdp8 faq (and I'm still working
on improving it).  Eventually, I'd like to see similar faq files
for a number of other old machines.  The next one I'd like to hammer
down is the IBM 701, a 1953 gem for which I happen to have the
principles of operation book.  If you like such things, here's a
brief summary:

Computer:     The IBM 701
Date:         1953
Technology:   Vacuum Tubes!

Size:         CPU -- about 9 to 10 feet wide, 6 feet high, 2.5 feet deep.
              Main Memory -- 4 or 5 feet wide; depth and height as above.
              
Main memory:  2048 words, 36 bits each, Williams tube technology.
Addressing:   word and half-word addressable.
		even negative numbers address words.
		even positive numbers address left-half-words.
		odd positive numbers address right-half-words.
Registers:    Accumulator -- 37 bits.
		two extra bits are provided for magnitude overflow.
	      MQ (multiplier-quotient) -- 38 bits.
		half-word loads and stores use the high 18 bits of registers.

Number system: Signed magnitude
	      Arithmetic assumes 35 bits right of the point.

Instruction:  18 bit (half word) instructions, formed as:

		sign of address | 6 bit opcode | 12 bit address

Instruction set:

        mnemonic opcode
	 R ADD     10      reset and add memory to accumulator.
	 ADD       09      add memory to accumulator.
         ADD AB    11      add absolute value of memory to accumulator.
         R SUB     06      reset and subtract memory from accumulator.
         SUB       05      subtract memory from accumulator.
         SUB AB    07      subtract absolute value of memory from accumulator.
         STORE MQ  14      store MQ in memory.
         ROUND     19      round accumulator by most significant bit of MQ.
         MPY       16      multiply MQ by memory giving result in AC-MQ.
	 MPY ROUND 17      multiply followed by round
	 DIV       18      AC-MQ div memory; MQ gets quotient, AC gets rem.
	 A RIGHT   23      Accumulator shift addr field places right.
	 A LEFT    22      Accumulator shift addr field places left.
	 L RIGHT   21      AC-MQ shift address field places to the right.
	 L LEFT    20      AC-MQ shift address field places to the left.
	 TR        01      Transfer control to the given address.
	 TR +      03      Transfer on accumulator positive.
	 TR 0      04      Transfer on accumulator zero.
         TR OV     02      Transfer on overflow and reset overflow indicator.
	 STOP      00      Stop, transfer to given address on restart.
	 STORE A   13      Store address field from high halfword of AC.
	 READ      24      Prepare to read one unit record from device.
	 READ B    25      Prepare to read one unit record backward.
	 WRITE     26      Prepare to write one unit record to device.
	 WRITE EF  27      Write end of file to mag tape unit.
	 REWIND    28      Rewind tape unit.
         SET DR    29      Set drum address of next unit record to read/write.
	 COPY      31      Copy one data word to or from unit record.
	 SENSE     30      Signal device and conditional skip on result.

Notes on instructions:

	Note the lack of procedure call instructions or provisions for
	array addressing!  The STORE A instruction was provided to allow
	easy construction of self-modifying code, and with careful self-
	modification, both could be accomplished.

	Note the lack of logical operations.  The importance of shifting
	was understood, but if you wanted to mask something, you had to
	shift one way and then the other, letting bits fall off the ends
	of the accumulator to clear them, and keeping in mind the extra
	two magnitude bits on the accumulator.

	Note that the mnemonics weren't designed for processing by an
	assembler.  Assemblers weren't routinely used yet, and programmers
	generally programmed in binary and then punched their programs
	in absolute binary on punched cards!  The manual includes a
	bootstrap loader that will load a single card image into memory,
	and then it includes a loader that fits on one-card to load a card
	deck full of code into memory.

	I have one used coding form from the MIT Digital Computer Laboratory
	that was apparently for this machine, and I have Diazo copies of
	other similar forms.  They never use the mnemonics given above!
	instead, they use cryptic two-letter abbreviations.

Unit record formats:

	80 column punched cards were handled as 12 rows of 72 columns, with
	each column stored in two consecutive memory locations, reading
	from the bottom of the card to the top.  A patch panel determined
	which columns the printer and punch would handle.

        The printer had 120 columns, with a character set of 48 characters.
	Output was in card image format, so no more than 72 characters
	could be printed per line.  A patch panel determined which 72.

        The magnetic tape drives stored data in 6 channels, with a 7th
        channel added for parity, all on half-inch wide tape with 1400
	feet of tape per reel.  This was the first computer to use this
	format, a format that lasted through the 1960's.

        The magnetic drum system stored 2048 words per drum, addressed
        by even integers as in main memory.  Words on drum are randomly
	accessable (within the limits of latency), with a set-drum-address
	command used to specify the starting drum address of each transfer,
	followed by a sequence of copy instructions to move the data.

	I/O instructions, particularly the copy instruction, were blocking,
	and would hang the CPU until the transfer was complete.

---

From: [email-masked] (Charles Lasner)
Date: 4 Sep 1993 03:46:27 GMT

In article <[email-masked]>,
Douglas W. Jones,201H MLH,3193350740,3193382879 <jones@pyrite> wrote:
>There were indeed more than a few errors in that newsletter!

Yes, as several people pointed out.  I have an additional criticism:

I truly believe in the intended cause the CHAC people are attempting, and
I really hope they succeed, but unfortunately, they seem to be victims of
their own predictions.  In order for such an organization to succeed, it
must *flawlessly* pursue its subject matter.

Towards that end, I would suggest that groups such as alt.sys.pdp8 act
as super-proof-readers of such material, i.e., post draft copies here first
and allow us pedantic pdp-8'ers and other interested hanger-outers to tear
apart their articles for technical accuracy, all in the interest of upping
the quality of the product, etc.

As it stands now, it's a little too revisional for me, although admittedly
only a little.  Forgive me for saying it, but from my vantage point, someone
who happened upon a 1401 in 1965 ain't a pioneer!  This is only marginally
before my time, and I already knew enough to know the mistakes pointed out
elsewhere, and I consider myself "second generation", not a true pioneer in
the industry, etc.

>
>1) The IBM 1401 was not a vacuum tube machine!  It was transistorized.

Amen!

And it always had all of the core memory present.  There was a jumper to
make half of the stack go away if the customer didn't pay for field service
for it!  (And sometimes a friendly tech could put it back in!)

>   TTL logic, with no computer.

Correct, Pong from Atari is a hard-wired TTL controller that plays a true
video game using digital techniques to accomplish all the features.  Contrast
that with the earlier Magnavox Odyssey which wasn't even a digital device.
Further, there is no provision to reprogram the device that Pong is, although
you can get into a grey area if something akin to a patch panel or even a
control ROM is used to transiently change the controller's exact function.
In any case, it still ain't a computer, since it lacks a program that can
be stored, nor has the storage itself to do such a thing either.  This is
also far afield from a true computer with a ROM-based program that as provided
cannot be changed without changing the ROM, because the ROM *could* be changed
if need be, and the changes could bring about either of two effects: 1) the
program could run the same way with totally different contents because it's
usually possible to program any reasonable task using entirely different
algorithms thus different, yet equivalent program sequences, or 2) The program
will run materially different if small changes to the code are made.  The
complications arise when a feature of the program is to sense external options
such as DIP switches or perhaps even semi-random input devices to determine
just what to do.  (Meaning that it's possible to use a computer to simulate
a hard-wired controller whose wiring gets patched, etc.)

>
>3) Spacewar wasn't a video game!  Video encoding of data was not used to
>   paint the image on the face of the CRT.  Instead, the software drove
>   a pair of ADC's to handle deflection in the X and Y directions, and
>   the software painted each dot on the screen.  The resolution was far
>   better than standard video, but the number of dots that could be
>   painted without causing flicker was limited.

This point is particularly galling as it's getting increasingly difficult
to explain to people that just because a screen lights up, it ain't gonna
necessarily be video!

The great thing about oscilloscope graphics is the random access aspect
of it.  Without having to rigorously display in raster order, you totally
avoid the jaggies, and most of these tubes use 12-bit D-A convertors to
make matters even better.  But when you don't use raster order, and instead
draw points where you want/need them, the jaggies just don't happen.  This
is why DEC has made various displays that were adequate with as little as
8-bits D-A convertors, and not the slightest aliasing visible on the
typical 'scopes used with them.  (Such as the LINC-8 or the AX08 with
various Tektronix scopes attached, etc.)

>
>(By the way, I have played spacewar myself on a DDP 224 computer at the
>University of Michigan -- that machine was a nice 24 bit minicomputer,
>and their version of spacewar used two joysticks on the graphics display.)

The description of the PDP-1 spacewar, clearly the first version, entirely
matches the 4K w/EAE PDP-8 version attributable to Richard Lary, Herb Jacobs,
and Rod Dorman, etc., which is usually distributed with P?S/8, which is able
to load it on a 4K PDP-8 it can run from, etc.

>
>In any case, the folks at CHAC clearly have their hearts in the right
>place, and the kinds of errors they made in their newsletter only serve
>to prove the point of their opening editorial!  History is indeed being
>lost and forgotten at an impressive rate!

Yes, if those who are committed to wanting to preserve history can't quite
get it together, we can't possibly succeed!  We must help these folks get
their act together completely.  All of us have a part to play to get it
correct, before the entire history of computing is personally attributed
to Bill Gates, now sometimes erroneously attributed to as the author of the
original BASIC among other things!

>				[email-masked]

cjl

---

From: [email-masked] (Charles Lasner)
Date: 4 Sep 1993 03:53:57 GMT

In article <[email-masked]>,
Douglas W. Jones,201H MLH,3193350740,3193382879 <jones@pyrite> wrote:
>of them sitting in my study right now at home!

And I (and Doug) collect computers that don't even have TTL in them, or even
the forerunner DTL chips either, or even RTL!  The original PDP-8, LINC-8,
various peripheral controllers, etc., are all made out of discrete components
meaning transistors, diodes, resistors, capacitors, a few pulse transformer
coils, a few oscillator crystals hooked to analog oscillator circuits made
of additional discrete components (years before the concept of the "oscillator
in a can"), etc.  Hundreds of little boards each stocked with a significant
quantity of some of all of the above only.

And surprisingly, the PDP-8/i, made mostly of TTL, isn't that much smaller,
in large part because the little boards are the limiting factor.  Most of the
M-series cards are empty real-estate, because for most cards, all of the
card-edge fingers are used up by the functionality of 3 TTL chips.  In the
R-series modules, even with 1/2 the fingers, the connectivity to density ratio
was more favorable.  Until DEC went to much larger modules, the fingers were
a long-standing bottleneck, etc.

cjl

---

From: [email-masked] (Travis Corcoran)
Date: Sat, 4 Sep 1993 01:36:09 GMT

My aptmate <[email-masked]> is the proud owner of a *WORKING* Pong
game.  Over the last few months we've played more Pong than...well,
we've played a lot of Pong...;) Somehow the classics never go out of
style... <attention marketeers: inser picture of
(Coke|chinos|jeans|etc.) here.>

--
__
TJIC (Travis J.I. Corcoran)         [email-masked]
          opinions(TJIC) != opinions(employer(TJIC))	

"It's like the '64 Air Force mission to the moon-you want to be on the
cutting edge, you gotta live with the secrecy."  
"What Air Force mission to the moon?"  
"See?"     -'In the Hole w/ the Boys w/ the Toys' G.Landis IAFSM Oct 93

---

From: [email-masked] (Travis Corcoran)
Date: Sat, 4 Sep 1993 01:37:27 GMT

My aptmate <[email-masked]> is the proud owner of a *WORKING* Pong

---

From: [email-masked] (Charles Lasner)
Date: 4 Sep 1993 07:02:35 GMT

In article <[email-masked]>,

>(Coke|chinos|jeans|etc.) here.>

Hmm...

Stories like this seem to cut down on some of the CHAC story about there
being only a few of them left?

cj "owner of less than 4,000,000 PDP-8's"

---

From: [email-masked]
Date: Sat, 04 Sep 93 08:13:14 EDT

>cj "owner of less than 4,000,000 PDP-8's"

Chill out dude, there's a difference between the coin-operated arcade
games that article was about, and the home version that you can get
anywhere these days for $15. Arcade games are "upgraded" to new games
by swapping the guts and putting new stickers on the outside, so most
of the early one are extremely rare now.

------------------------ uunet!quack!gilly!dave ------------------------
================= Dave Fischer - Nature's Perfect Food =================
----------------------- [email-masked] ------------------------

---

From: [email-masked] (Ethan Dicks)
Date: 4 Sep 93 23:21:01 EDT

Charles Lasner ([email-masked]) wrote:

: Correct, Pong from Atari is a hard-wired TTL controller that plays a true
: video game using digital techniques to accomplish all the features.  Contrast
: that with the earlier Magnavox Odyssey which wasn't even a digital device.

I just unpacked my old Magnavox, complete with the plastic colored screen
overlays (in two sizes) for adding boundaries and other features to the games.

I have dissected in more than once (and it still works :-), and can confirm
personally that it is a strictly analog device.  The motherboard is populated
with edge-card connectors which are filled with 2"x2" circuit boards to perform
things like horizontal timing, vertical timing, dot generation, drift, etc.
The specifics of the game (control of the ball, display of paddles, response
on collision detection, etc.) are selected by plugging in a "cartridge".  This
cartridge contains no active components, but rather jumpers various pins of
the 44 pin connector, turning on or turning off various features.  To play
a game, you tape the correct colored overlay to the screen and plug in the
correct cartridge.

Stone knives and bearskins.

-ethan

---

From: [email-masked]
Date: 7 Sep 93 07:38:38 -0400

> things like horizontal timing, vertical timing, dot generation, drift, etc.

If it's putting dots on the screen (and if it contains TTL!), it's probably not
an analog device.  I suspect you mean that it does not contain a microprocessor
or a semblance thereto.

---

From: jones@pyrite (Douglas W. Jones,201H MLH,3193350740,3193382879)
Date: Tue, 7 Sep 1993 14:33:07 GMT

>From article <[email-masked]>,
by [email-masked]:
> 
> If it's putting dots on the screen (and if it contains TTL!),
> it's probably not an analog device.  I suspect you mean that
> it does not contain a microprocessor or a semblance thereto.

No, the point is that the Magnavox Odyssey used analog techniques
to drive the logic of the game.  No doubt there were some digital
signals inside, in the sense of saturating transistors and on-off
logic, but the basic mechanisms that moved the ball on the screen
were analog.  For an example of the kinds of things that go into
an analog video game, consider the use of current sources and
integrators instead of clocked counters to determine the X and Y
positions of the "ball" on the screen.  The decision to illuminate
the dot on the screen then rests on an analog comparitor that
compares the outputs of these integrators with the outputs of
another pair of integrators that effectively track the current
coordinates of the video scan on the display screen.  Sure, there
may be one and gate used to determine that both X and Y coordinates
match, but the heart of the computation is analog!

				Doug Jones
				[email-masked]

---

From: [email-masked] (Charles Lasner)
Date: 7 Sep 1993 16:46:49 GMT

In article <[email-masked]>,
>> it does not contain a microprocessor or a semblance thereto.

No, Nein, Nyet!  There is nothing in the remotest sense digital about this 
device!!!!!  There are no gates whatsoever.  All is done with analog
comparators including the gating on of the moving dot which unblanks the
video directly at the tracked location which is determined as Doug says,
which itself is an analog comparison.

>match, but the heart of the computation is analog!

Even that is done by two analog comparators.  These people went out of their
way to avoid digital.  (I was part of the expert witness consultancy on a case
directly concerned with this aspect.  The Odyssey was covered by an overly
broad patent that doesn't distinguish between a digital and an analog
implementation.  The case wasn't broken on this ground however, instead we
got 'em on prior art using the PDP-8!)

>				[email-masked]

DEC uses an analog comparator to do the select logic on the TU55/TU56
DECtape connected to controllers such as the TC01/TC08.

Every DECtape drive has a connection to a line called SELECT ECHO.  It is
driven with a DEC standard relay driver card which has predictable analog
characteristics.  When not selected, the driver contributes only a negligible
leakage current, but when selected, the driver transistor is driven only into
the active region.  (Normally, this card, with a large output transistor, is
meant to drive some large contactor relay coil or other multi-amp load, but
in this application, it is "loafing" and driving a 1/4W resistor.)

In the TU55, the relay driver module is of course driven by negative logic
signals.  In the TU56, the relay driver module is a newer card that is
driven by TTL signals, but is otherwise the same design.  (DEC had a habit
of updating certain stock module designs for specific purposes.  The TTL
version of the relay module is essentially the original card with a level
converter on the card.)  Thus, it is perfectly OK to mix systems where
some drives are TU55 and some are TU56, etc.

So, there are up to 8 possible drives with individual relay drivers connected
to SELECT ECHO.  Within each tape controller there is an analog comparator
connected to that line, along with the modest load resistor.  When one drive
selects, the resultant voltage is predictably within a narrow tolerance range.
It will be too high if no drives select, and too low if 2-8 drives select.
Thus, the analog comparator's output is used to create the internal signal
called SELECT ERROR.

The same "logic" is used to drive the WRITE ECHO signal.  IFF there is not
a SELECT ERROR condition, then another comparator checks the voltage on
WRITE ECHO.  Of course that signal could only be in two states, i.e., not
driven or driven by the selected drive (or overdriven by too many drives,
but then SELECT ERROR is set invalidating the WRITE ECHO signal).

Thus, there is a purely analog interface between the drives and the controller
on not only the head data, but also the select and write-protect logic.  The
command logic does use logic levels to control motion of the motors.  For the
TU55, either the old "relay" levels or negative logic levels are used, and
the construction of the TU55 is all R-series logic, with an optional card to
level convert from relay -> negative if needed in an older system (such as
a 555 DECtape system.  The TU55 was originally called the "Solid-State
DECtape Drive".).  The TU56 accommodates all of that, and additionally uses
an additional level converter because it can also be driven by TTL levels.
The TTL levels are used in the TD8E and the TC-11.  The negative levels are
used in the TC01, TC08, TC12, TC02, TC15, etc.  (The last two are the PDP-9
and PDP-15 controllers respectively.)

cjl

---

From: [email-masked] (Kip Crosby)
Date: Tue, 07 Sep 1993 00:43:49 GMT

In article <[email-masked]>, Douglas W. Jones,201H MLH,3193350740,3193382879 (jones@pyrite) writes:
>  [....arcana deleted....]
I don't have my copy of Goldstine's _The Computer from Pascal to
von Neumann_ right to hand (chorus of "Why NOT?!",) but I think von
Neumann, Adele Goldstine and Arthur Burks actually _did_ do that. 
If I can dig up ch. and verse I'll be back with it.

__________________________________________
Kip Crosby         [email-masked]   
Computer History Association of California 
     "History is what you make it...."

---

From: [email-masked] (Kip Crosby)
Date: Tue, 07 Sep 1993 01:00:52 GMT

>of some of these early computers ( especially the programmable ones ).
ENIAC had 20 ten-decimal-digit words in valves, 100 ditto in mag
core, 304 ditto in a func. table, 96 in the patch panel, and 8 in
mag relays as a single-card cache.  There were 97 instructions of 2
decimal digits each, with 5 or 6 instructions per word (there were
some 12-digit words,) and fixed-decimal arithmetic.  I/O was by
IBM 80-col card at 125 cards/min I and 100 cards/min O.

All of this and much more is in:

_Historical Dictionary of Data Processing_
James W. Cortada
Greenwood Press, Westport, CT, USA

which is three hardcover volumes, Technology, Biographies, and
Organizations.  Invaluable for the historian, fascinating reading,
best for stuff before 1980, and (this is the hard part) about
US$150 the set -- but you can buy the individual volumes.

Cheers,

---

From: [email-masked] (Kip Crosby)
Date: Tue, 07 Sep 1993 13:25:08 GMT

>the quality of the product, etc.

We're delighted to have super-proofers -- that's a lot of why we're
on USENET to begin with.  Tear away!  (Not that people haven't.) 
On the other hand, I will concede (being one) that editors are
human, and no less fallible in that capacity than in any other;
flawless pursuit of subject matter is perennially desired and less
often attained.  If we publish articles that need no correction,
great.  If our articles go out to readers and somebody finds a
bug, then, to publish the article _and_ the correction still does a
service to the community and enriches the public record.  When the
October ENGINE appears you'll see that we do publish corrections,
even at a length that will surely satisfy the most pedantic. 

>elsewhere, and I consider myself "second generation", not a true pioneer in

I don't quite get the intent of the word 'revisional', but in any
case, certainly "someone who happened upon a 1401 in 1965 ain't a
pioneer."  IBM announced the 1401 in October 1959 and, in fact,
projected in an internal report that the end of the useful life of
the series would occur in 1965.  But while pioneering work is
important to CHAC, and preserving the record of it is an important
part of our mandate, it ain't the whole story, either.  If
somebody can make an interesting, illuminating point about computer
use in California, at the appropriate length, then it doesn't
matter whether they were the first to gain experience with a
system or (as might be equally intriguing) the last.

>original BASIC among other things!

I wouldn't worry about billg getting _all_ the credit.  He was born
in the year that the first IBM 704 was delivered, so vacuum-tube
computing is probably safe from the attribution :-)

---

From: [email-masked] (Stephen Wolfson)
Date: Tue, 7 Sep 1993 18:27:05 GMT

Well as I recall there was an article in IEEE on constructing a pong game.
So look up back issues circa '75-76.  

Now then where did I put my old TV Typewriter terminal :-)

---

From: [email-masked] (young a t)
Date: 7 Sep 1993 19:05:15 GMT

In article <[email-masked]> [email-masked] (Douglas W. Jones) writes:
|>for a number of other old machines.  The next one I'd like to hammer
|>down is the IBM 701, a 1953 gem for which I happen to have the
|>principles of operation book.  If you like such things, here's a

Hey -- maybe you're the person to answer my perpetual query about the Q bit!

...
|>Registers:    Accumulator -- 37 bits.
|>		two extra bits are provided for magnitude overflow.
                ^^^^^^^^^^^^^^
That sounds like the 704's AC: 35 bits + S,P,Q

|>	      MQ (multiplier-quotient) -- 38 bits.

??? Really?  Not 36?  The 704 MQ had 36.

|>Number system: Signed magnitude
|>	      Arithmetic assumes 35 bits right of the point.

I believe floating-point came in with the 704.  People wrote "fixed-point"
arithmetic routines for these machines, assuming the binary point was at
some conventional place (left end, right end, or middle) of the word.  Even
wrote square-root routines and trig functions for fixed-point arithmetic.

...
|>Notes on instructions:
...
|>	Note the lack of logical operations.  The importance of shifting
|>	was understood, but if you wanted to mask something, you had to
|>	shift one way and then the other, letting bits fall off the ends
|>	of the accumulator to clear them, and keeping in mind the extra
|>	two magnitude bits on the accumulator.

Yeah.  Same problem with shifting the 704 AC.  The Q bit would get you
every time.
...
|>Unit record formats:
|>
|>	80 column punched cards were handled as 12 rows of 72 columns, with
|>	each column stored in two consecutive memory locations, reading
|>	from the bottom of the card to the top.  A patch panel determined
|>	which columns the printer and punch would handle.

Which is why FORTRAN statements only used the first 72 columns.

|>        The printer had 120 columns, with a character set of 48 characters.
|>	Output was in card image format, so no more than 72 characters
|>	could be printed per line.  A patch panel determined which 72.

Yes; but if that was the same printer the 704 used, you could then print the
rest of the 120 columns on a second print cycle.  Took a special wiring panel
to read the sense magnets back to the CPU, though.

|>        The magnetic tape drives stored data in 6 channels, with a 7th
|>        channel added for parity, all on half-inch wide tape with 1400
|>	feet of tape per reel.  This was the first computer to use this
|>	format, a format that lasted through the 1960's.

You left out the density: 200 bpi.  There used to be "tape developer fluid"
you could buy that had little black magnetic particles suspended in something.
Dip the tape in, and the bits turned black.  After the solvent evaporated, you
could lift them off with Scotch tape and read the bits from a damaged piece of
mag tape.

|>        The magnetic drum system stored 2048 words per drum, addressed
|>        by even integers as in main memory.  Words on drum are randomly
|>	accessable (within the limits of latency), with a set-drum-address
|>	command used to specify the starting drum address of each transfer,
|>	followed by a sequence of copy instructions to move the data.
|>
|>	I/O instructions, particularly the copy instruction, were blocking,
|>	and would hang the CPU until the transfer was complete.

Sounds just like the 704 in that respect.  The Load-button sequence was:

select card reader
copy 9-left word to absolute address 0
copy 9-right word to absolute address 1
transfer control to location 0

Those first 2 words from the loader card had to read in the rest of the card,
which had to read in the rest of the program.  We had very thin bootstraps
in those days....

It used to be a game to see if you could write an input-conversion routine fast
enough to convert & store a card's worth of data before the card reader needed
another "select" instruction.  If so, you could keep the card reader running at
its full speed of 90 cards/minute.  If not, you lost a whole cycle, and the 
reader went CHUNK. CHUNK. CHUNK. instead of slurp slurp slurp....

The catch was that cards were punched column-wise, but read row-wise; so you
had to read the *whole* card and rearrange all the bits just to read the 72
characters.  Converting characters to binary representation took more time on
top of that.

A big speedup came with the 7090, which used Data Channels for I/O instead of
having to synchronize the program with the rotation of the hardware.
-- 
A.T.Young                      [email-masked]
Astronomy Department
San Diego State University
San Diego CA 92182-0540

---

From: [email-masked] (Kip Crosby)
Date: Tue, 07 Sep 1993 21:17:09 GMT

In article <[email-masked]>, Charles Lasner ([email-masked]) writes:
>>game. 
We weren't talking about the one that was sold commercially to
attach to your TV, but about the original arcade version in the
big plywood box.  The figure of nine is from a source at the
American Museum of the Moving Image, which owns one.

---

From: [email-masked] (Kip Crosby)
Date: Wed, 08 Sep 1993 12:27:57 GMT

>of the early one are extremely rare now.

My point exactly.                                    --  kc

---

From: [email-masked] (Ethan Dicks)
Date: 10 Sep 93 08:59:40 EDT

[email-masked] wrote:
: In article <[email-masked]>, [email-masked] (Ethan Dicks) writes:

[ Discussion of Odessey deleted ]

: If it's putting dots on the screen (and if it contains TTL!), it's probably not
: an analog device.  I suspect you mean that it does not contain a microprocessor
: or a semblance thereto.

I mean what I said!  I never said that it contained TTL parts of any kind.  I
said that the Odessey is an analog device.  TTL is not required to put dots
on the screen. neither is a microprocessor.

If there are any ICs on the main board, they are Linear, not TTL.

-ethan

---

From: [email-masked] (John West)
Date: 12 Sep 1993 10:57:19 GMT

>principles of operation book.  If you like such things, here's a

PDP1, anyone? I've got a heap of manuals and things (from an
emulator/clone project I'm working on). The following is from memory, so it
is incomplete and probably incorrect.

Computer:     PDP1
Date:         erk. I've forgotten. 1960 is not more than 3 years away.
Technology:   Transistors

>Main memory:  4096 words of 18 bits. Ferrite core. Memory extension box
	       gives 65536 words of 18 bits and changes operation of some
	       instructions to address it.
>Addressing:   words
>Registers:    AC: 18 bits
               IO: 18 bits
	       6(?) flag bits

Number system: One's complement. 18 bits

Instruction:  18 bits. Mostly 6 bits of opcode followed by 12 bits of
              address. Low bit of opcode is 'indirect' bit - operand is at
	      location pointed to by the location given in the instruction.
	      Some instructions use the address field as a micro-code
	      instruction. Various bits control various operations. Opcode
	      72(?) is for IO - address specifies what operation to do.
	      IO instructions depend on what extra boxes you have plugged
	      in. Most instructions take 10us.
	      Core memory is inherently RMW, and instruction set takes
	      advantage of this - you have 'store instruction part' and
	      'store address part' instructions for self modifying code. No
	      stack. Subroutine call places old PC into AC. 

Wonderful vector displays that put this VGA rubbish to shame. The cheap one
was addressable to 1K*1K. Vector so no jaggies on your lines. You could buy
a character generator box that drew 5*7 characters in one of 4 sizes, and
could cope with 200 or so without flickering.

I'm very impressed at how fast it was. 10us doesn't sound like a
particularly speedy instruction, but if you compare it to things like the
6502 (nearly 20 years later) with an average 4us per instruction, it is
quite good. With the multiplier option, you could multiply 18 bit words in 
under 25us.

John West

---

From: [email-masked] (David Turner)
Date: 13 Sep 93 03:47:00 GMT

J>PDP1, anyone? I've got a heap of manuals and things (from an
 >is incomplete and probably incorrect.

Just because I am insanely curious, what exactly is it that you are
working on? A PDP-1 emulator? What would you run it on? Is it near
completion? How in the world did you find manuals and stuff for it?

I would love to hear more... if you don't want to post too much on the
topic, I would be happy to swap e-mail.

Regards, ** David Turner **

---
 ~ QMPro 1.0 00-0000 ~ Misspelled?  Impossible.  My modem is error correcting.

---

From: [email-masked] (Sean Case)
Date: 18 Sep 93 05:23:02 GMT

[email-masked] (young a t) writes:

>                                    There used to be "tape developer fluid"

The hardware people where I work still use it... it's one way of checking
the head alignment on the tape. I don't think they've tried recovering
data with it.

The other thing it's good for is demonstrating how tape works to trainees.

Sean Case
--
Sean Case                  [email-masked]
"The day is surely coming when bank robbers will
plead in mitigation that the getaway car had its
hazards on." -- Ben Elton, _Gridlock_

---

From: [email-masked] (Charles Lasner)
Date: 18 Sep 1993 05:38:27 GMT

>>you could buy that had little black magnetic particles suspended in something.

Reeves-Soundcraft "Magnasee" was a brand of the stuff with the ferrite
suspension in it dissolved in Carbon Tet.  It evaporates and shows you the
flux pattern, etc.

It was also useful for quarter-track audio tape to see if the height adjustment
was reasonable on the head before azimuth adjustments were made.  On some
tape decks, the azimuth adjustment might interact with height, so you had to
check the final alignment with the liquid stuff, etc.

cjl

---

From: [email-masked] (Paul Repacholi)
Date: 19 Sep 93 05:43:01 +0900

> the head alignment on the tape. I don't think they've tried recovering

Where do they get it from? I need some for head alighnments, and can't
find any.

~Paul

---

From: [email-masked] (DoN. Nichols)
Date: Mon, 20 Sep 1993 00:14:57 GMT

>Where do they get it from? I need some for head alighnments, and can't

	Well ... what I have, _Mag View_ I obtained from Saxitone Tape Sales
in the Washington D.C. area a few years ago, but they have gone out of
business.

	It is in an aerosol can, labeled "Magnetic Tape Track Developer",
and was manufactured/packaged by Nortronics, the company that makes
replacement tape heads for almost any flavor of audio tape drive.  The part
number on the can is QM601, and contains 4 Oz. of TrichloroTrifloroEthane
and Iron Power based on the label.  It might be more difficult to get these
days, with the increased concern about chloro-fluoro-carbons.  It doesn't
take much, so I have had many years of use from it.  (I also don't need to
use it often.)

	Good Luck
		DoN.
-- 
 Email:   <[email-masked]>  |  ...!uunet!ceilidh!dnichols 
		 <[email-masked]>
 Donald Nichols (DoN.)  |   Voice (Days): (703) 704-2280 (Eves): (703) 938-4564
	--- Black Holes are where God is dividing by zero ---

---

From: [email-masked] (Brian Murray)
Date: Tue, 21 Sep 1993 07:49:23 GMT

>Now then where did I put my old TV Typewriter terminal :-)

Around that time some clever sod put the whole pong game on a single
chip and called it the AY-3-8500 (from memory). There were a number of
projects in magazines that used that chip, and it is the basis for the
commercial home TV pong games everyone has in a box in the back of the
cupboard. Perhaps the IEEE article used this chip?

P.S. has anyone got the schematics of the original TTL pong game? 

-- 
------------------------------------------------ Brian Murray ---
[email-masked]  CBX250  Apple//c  VAX 11/750  SGI Indigo
-----------------------------------------------------------------

---

From: [email-masked]
Date: 24 Sep 93 13:45:55 +0930

> suspension in it dissolved in Carbon Tet.  It evaporates and shows you the

Carbon Tet ?  I would have expected the tape to dissolve !

We had a little gadget once with the fluid between two plates of glass, less 
messy and reusable.  It was about the size of a small compass.

Regards,

John Bennett                                   [email-masked]
Head, I.T. Services Development                Phone : +61 8 259 5292
Corporate Information Systems                  FAX   : +61 8 259 5537
DEFENCE SCIENCE AND TECHNOLOGY ORGANISATION    Postal: Bld 73 Labs Area
AUSTRALIA                                              PO Box 1500 Salisbury 
                                                       South Australia  5108
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