[GTALUG] ancient computer history

[D. Hugh Redelmeier via talk]

I read this with fascination in 1967 or perhaps early 1968. It was almost
current then! Looking at it now, I still remember some of the phrases.

<https://www.computer.org/web/csdl/index/-/csdl/proceedings/afips/1964/5064/00/50640001.pdf>

(I was in high school then and it was extremely difficult to get
information about computers then. The internet is such a great facility!
I used to sneak into U of T, Waterloo, and York to get accesss to
computers.)

It's fun to read of Algol's support for recursion and dynamic memory
allocation of local variables:

it is fair to say that they are difficult, and their inclusion in
an Algebraic lanuage that is intended to be universal is
controversial.

How far have we come!

(How did I end up on this page? I posted a link to the Algol 60 report to
the list. The report is dedicated to the memory of William Turanski who
was killed before the conference. I've always wondered who he was. It
turns out that he worked with Anatol Holt on an early programming system
for the US military. He also was a Putnam Fellow (undergrad math
contest). Turanski is mentioned in Rosen's paper.)
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[James Knott via talk]

Post by D. Hugh Redelmeier via talk
I read this with fascination in 1967 or perhaps early 1968. It was almost
current then! Looking at it now, I still remember some of the phrases.
<https://www.computer.org/web/csdl/index/-/csdl/proceedings/afips/1964/5064/00/50640001.pdf>

I've long been interested in computer history.  Several years ago, I
read a book about early IBM computers, going back to the invention of
Hollerith cards.  I have also worked on some old gear.  Many years ago,
I worked on a system in the Toronto Stock Exchange on Bay St.  This
system, made by a company called "Teleregister" was a single purpose
computer, built with vacuum tubes, relays and a memory drum.  It was
older than I was.  There was another system at my company, made by
Phillips, that used a slightly tapered memory drum.  One feature of this
drum was that as it spun up, it would rise, bringing the drum close to
the heads.  If power failed, it had a fail safe mechanism to move the
drum away from the heads, gravity.  I also used to maintain a PDP-8i
computer.  When browsing through the programming manual, I found DEC
actually recommending self modifying code, to get around the limitations
of the instruction set!  I also worked with Data General Nova and
Eclipse computers which had something I have not seen elsewhere.  That
is auto increment and decrement indirect addressing.  This involved
address locations, that when used for indirect addressing, would
automagically increment or decrement.  These older computers used core
memory and the video terminals connected to the Nova computers used
acoustic delay lines for memory.  The terminals connected to the PDP-8
used core memory.  I also used to work with mag tape stands and punch
card equipment.  I also used to work with the Datapoint 2200 smart
terminal, which the Intel 8008 CPU was intended for, but they went with
their own CPU board because the 8008 didn't have adequate performance. 
However, it retained the 8008 instruction set.  Back in those day, I
already owned an IMSAI 8080 computer, with the Intel 8080 CPU.



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[Stewart Russell via talk]

Post by James Knott via talk
I also used to maintain a PDP-8i
computer. When browsing through the programming manual, I found DEC
actually recommending self modifying code, to get around the limitations
of the instruction set!

The basic PDP-8 didn't have a hardware stack, so you had to prepare
subroutines by modifying the code's return address before you called it.

I'm building a PDP-8 compatible right now, based on the Harris HD-6120
"PDP-8 on a chip" used in the DECMate desktops. I'd best brush up my octal,
as it's a 12-bit machine.

Cheers
Stewart

[Scott Allen via talk]

Starting yet another "I remember, back in the day" thread, are we? Let's
see how far this one goes. :-/

[James Knott via talk]

 I also used to maintain a PDP-8i
computer.  When browsing through the programming manual, I found DEC
actually recommending self modifying code, to get around the limitations
of the instruction set!
The basic PDP-8 didn't have a hardware stack, so you had to prepare
subroutines by modifying the code's return address before you called it. 
I'm building a PDP-8 compatible right now, based on the Harris HD-6120
"PDP-8 on a chip" used in the DECMate desktops. I'd best brush up my
octal, as it's a 12-bit machine. 

Being a hardware tech, I didn't really get into software.  However, I
found on my IMSAI, with the 8080 CPU, working in octal was better than
hex, as the digits lined up with the instruction fields.  They didn't
with hex.

I just tried to dig up an article I read in Byte magazine about that
chip, but couldn't find it.  However, I did find an article that, in
addition to mentioning the PDP-8, included this:

And Ethernet's Fate?
A report issued by Strategic Incorporated, a market-research firm in San
Jose, California, predicts Xerox Corporation's  Ethernet local-area
network will be a total failure within two years. According to
Strategic's president, Michael Killen,  "Xerox is headed for the worst
failure in the company's history." He believes that Xerox lacks
technological and price advantages, sales force, and customers
interested in buying large systems.   Further,   he contends that
Ethernet's baseband approach to local networking will prove inferior
over the long haul to the broadband approach taken by Xerox's
competitors.   He points out that broadband systems are better suited to
carry video, heavy voice and data transmissions, among other
applications. In response to the report, Xerox issued the following
statement:
" Based on the level of customer satisfaction with our existing network
installations, the backlog of orders for network products and service,
and the interest in Ethernet on the part of major accounts,  we are
confident that Xerox will be a leading vendor in office automation."


I suspect that report was a bit off the mark!  ;-)

https://tech-insider.org/personal-computers/research/acrobat/8203.pdf
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[James Knott via talk]

Post by Stewart Russell via talk
The basic PDP-8 didn't have a hardware stack, so you had to prepare
subroutines by modifying the code's return address before you called it. 

The Data General Nova didn't either.  The Eclipse did.

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ta

[D. Hugh Redelmeier via talk]

| From: Stewart Russell via talk <***@gtalug.org>

| On Tue, Sep 18, 2018, 10:48 James Knott via talk, <***@gtalug.org> wrote:
|
| > I also used to maintain a PDP-8i
| > computer.

I used PDP-8s and PDP-8i computers that I found access to at the U of
T in 1968 and 1969 (when I was sneaking in). Let me be clear: as far
as I know, I wasn't breaking any rules because nobody thought to make
such rules. It did mean that I was careful not to get in anyone's
way. I actually wrote some code for some of the real users.

The PDP-8s was meant to transcribe paper tape to magnetic tape. I
think it was for bubble-chamber experiments. I don't think I ever saw
any users for it.

It had no disk drive and I didn't know how to use the tape drive.

If the physicists knew more about the PDP-8s, they should have been
clamouring for access to run FOCAL-8 (kind of like BASIC) as a
programmable calculator. I don't think they had access to an interactive
computer in those days.

The PDP-8i was meant to be part of a hybrid computer (analogue +
digital). I never used the analogue part (what's an op amp?).

You can see that these were the embedded computers of the day. There
wasn't a cheaper or more convenient (no airconditioning required) thing
that we'd call a computer.

| > When browsing through the programming manual, I found DEC
| > actually recommending self modifying code, to get around the limitations
| > of the instruction set!

One of the best things about the PDP-8 were the comprehensive manuals
(one for each year). I still have them somewhere. They took you from
zero to programming for the real machine, all in a trade paperback
sized book. They were widely available.

The PDP-8's instruction set was extremely simple. I still remember
much of it.

| The basic PDP-8 didn't have a hardware stack, so you had to prepare
| subroutines by modifying the code's return address before you called it.

Close, but not exactly.

JSR X
would put the address of the next instruction after the TSR into
location X and then jump to X + 1, the next word. An address fits in
a single 12-bit word.

The subroutine would return via
JMP I X
That would jump to the address contained in X.

So all the book-keeping was done in that simple pair of instructions.

The normal way of passing a parameter was the accumulator. Beyond
that, you'd put addresses after the call instruction. That required a
bit of toing and froing. Global variables were used heavily instead.

Recursion and re-entrancy? Not so easy. But remember the quote I posted
about recursion. It was still avant-garde in the 1960s.

Many earlier "big" computers had similar call instructions. The first
calling sequence that I learned of that left the return address in a
general register was on the IBM System/360. And the conventional ABI
didn't include a stack. The PDP-10 had clean (new: PUSHJ/POPJ) and
dirty (backward compatible: JSR/JRST) linkage instructions.

Hardware was under control of oligopolies. This held innovation back.
DEC was an insurgent.

Burroughs' architectures were brilliant and odd but didn't get much
traction.

| I'm building a PDP-8 compatible right now, based on the Harris HD-6120
| "PDP-8 on a chip" used in the DECMate desktops. I'd best brush up my octal,
| as it's a 12-bit machine.

Three hex digits, no?

But yes, the PDP-8 really is most natural in octal. The primary
opcode is the first octal digit.
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[James Knott via talk]

Post by D. Hugh Redelmeier via talk
The PDP-8i was meant to be part of a hybrid computer (analogue +
digital). I never used the analogue part (what's an op amp?).

As far as I know, the PDP-8i I worked on didn't have any analog
hardware, though it might have been available as an option.  Many years
ago, analog computers were often used in science and engineering, as
digital computers weren't fast enough.  Of course an analog computer was
useless for business use, where you need accurate results and not just
so much precision.  Op amps are high performance amplifiers, with
characteristics primarily controlled by components in the feed back
loop.  For example, it possible to determine exponents or logs, just by
adding a diode to the feedback loop, in the appropriate manner.  It's
also easy to create a summing circuit, by using multiple input
resistors.  Op amps are still commonly used in instrumentation, servos,
etc..

Incidentally, those mini-computers, from DEC, Data General, etc. often
had prototyping boards available, which could be used to build any
custom interface that might be needed in a lab, factory, etc..


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[D. Hugh Redelmeier via talk]

| From: James Knott via talk <***@gtalug.org>

| On 09/18/2018 07:11 PM, D. Hugh Redelmeier via talk wrote:
| > The PDP-8i was meant to be part of a hybrid computer (analogue +
| > digital). I never used the analogue part (what's an op amp?).
|
| As far as I know, the PDP-8i I worked on didn't have any analog
| hardware, though it might have been available as an option.

Sorry that I wasn't clearer. The particular PDP-8i that I used was
wired to an analogue computer. I don't really remember the name of
the analogue computer.

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[James Knott via talk]

Post by D. Hugh Redelmeier via talk
(I was in high school then and it was extremely difficult to get
information about computers then. The internet is such a great facility!
I used to sneak into U of T, Waterloo, and York to get accesss to
computers.)

I didn't have access to computers until I bought my own, an IMSAI 8080,
in 1975.  However, when I was in Gr. 12, I took a FORTRAN course.  We
used pencil mark cards, which our teacher took to the board office to
compile.  I don't know that the code was actually run.  We were more
focused on getting back results showing it had compiled correctly.  I've
often thought that we could have written nonsense code, provided it
compiled correctly.  ;-)

I also took a FORTRAN course at Ryerson, back in the mid 80s.  In class,
we had to find a working terminal, that was connected to an IBM
mainframe.  I found it easier to my homework on a VAX 11/780 at work. 
So, when the lab portion of the class started, I'd go home, dial into
the VAX using my IMSAI, and do my homework that way.  This was also
around the time Ryerson stopped using punch card equipment, connected to
a computer at York.  I recall seeing that equipment, forlornly sitting
in the hall, disconnected from any computer.  :'(

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