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.)
On 09/18/2018 02:37 AM, D. Hugh Redelmeier via talk wrote:
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.
On Tue, Sep 18, 2018, 10:48 James Knott via talk, <talk@gtalug.org> wrote:
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
Starting yet another "I remember, back in the day" thread, are we? Let's see how far this one goes. :-/ -- Scott
On 09/18/2018 12:43 PM, Stewart Russell via talk wrote:
On Tue, Sep 18, 2018, 10:48 James Knott via talk, <talk@gtalug.org <mailto:talk@gtalug.org>> wrote:
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
| From: Stewart Russell via talk <talk@gtalug.org> | On Tue, Sep 18, 2018, 10:48 James Knott via talk, <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.
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. 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..
| From: James Knott via talk <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.
On 09/18/2018 02:37 AM, D. Hugh Redelmeier via talk wrote:
(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. :'(
participants (4)
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D. Hugh Redelmeier -
James Knott -
Scott Allen -
Stewart Russell