[HN Gopher] Reverse-engineering a mysterious Univac computer board
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Reverse-engineering a mysterious Univac computer board
Author : picture
Score : 87 points
Date : 2022-04-03 17:15 UTC (5 hours ago)
(HTM) web link (www.righto.com)
(TXT) w3m dump (www.righto.com)
| tyingq wrote:
| The real-life "spaghetti code" visual is pretty neat:
| https://upload.wikimedia.org/wikipedia/commons/b/b7/IBM402pl...
| zw123456 wrote:
| Always thanks to Ken for all the fun "memory" lane stuff.
|
| That board reminded me of an old PDP1 board from way back when I
| was doing undergrad in the 1970's and we had a "junker" PDP1 that
| no longer ran (replaced with new PDP8) but people would salvage
| things off it. It had that same old timer Resistor, Diode,
| Transistor type logic circuits on it.
|
| Would love to see some of the old PDP's stuff reversed engineered
| if they have any of it around there. Ken if you take requests :)
| quercusa wrote:
| That plugboard brings back long-suppressed nightmares of bad
| wire-wrapping jobs.
| GrumpyNl wrote:
| I still have one, given to me by IBM. Nice decoration piece.
| marcodiego wrote:
| "many customers found plugboard programming easier than
| programming with code, both because they were more familiar with
| it and because it is visual and direct."
|
| If your program has only 31 steps, I'd also would prefer to
| program it using a plugboard panel.
| rep_lodsb wrote:
| Seems like it quickly turns into spaghetti code:
|
| > https://static.righto.com/images/univac-board/plugboard.jpg >
| A plugboard for the Univac 1004. This board was used for
| payroll consolidation from 1965 to 1972.
| aftbit wrote:
| Today I learned about excess-3 encoding, from footnote 10 in the
| linked article. Its interesting to see how clearly the early
| computers were intended to work with decimal while retaining the
| simplicity brought by using the two signal levels of binary.
| Footnote reproduced here:
|
| The computer uses excess-three encoding for digits, adding 3 to
| the value before converting to binary. For example, 6 is
| represented as binary 1001. The advantage of this encoding is
| that flipping the bits yields the 9's-complement decimal value,
| simplifying subtraction. For example, flipping the bits of 6
| yields binary 0110, which is 3 in excess-3 notation. Excess-3
| representation also handles carries correctly; if you add two
| numbers that sum to 10, the excess-3 values will sum to 16,
| causing a binary carry. To convert the sum to excess-3, The value
| 3 must be added (if a carry) or subtracted (if no carry).
|
| To see how addition works with excess-3, 2 + 4 in excess-3 is
| binary 0101 + 0111 = 1100. Subtracting 3 yields 1001, which is 6
| in excess-3. But 2 + 9 is binary 0101 + 1100 = 10001, generating
| a carry out of the 4 bit value. Adding 3 yields 0100, which is 1
| in excess-3. Considering the carry-out, this is the desired
| result of 11.
| kragen wrote:
| Some early computers, as early as the 01940s, used binary;
| others used decimal, typically BCD but sometimes excess-3 BCD
| or one-hot encoding. Knuth's MIX was originally specified to be
| either binary _or_ decimal, as you prefer, but by the later
| volumes of TAOCP he switched to requiring binary for things
| like tries.
|
| Typically an early (pre-01960) computer was either "scientific"
| or "business". A "scientific" computer was binary, had word-
| oriented memory of at least 16 bits width and sometimes as much
| as 60 or more, was measured by its calculation speed, and had
| floating point. (Some didn't even have separate integer
| arithmetic.) A "business" computer was decimal, had character-
| oriented memory of 6-9 bits, was measured by its I/O speed, and
| had only integer arithmetic, or not even that (as in the case
| of the IBM 1620). These categories were blurring a lot by the
| 01960s, and the IBM 360 largely put an end to the division: it
| had 8-bit-wide memory, 32-bit-wide CPU registers, floating
| point and binary integer and binary decimal arithmetic, and
| different binary-compatible models with varying degrees of
| speed at I/O and calculation. A few years later there were even
| models that supported paging and timesharing.
| rst wrote:
| The 1620 was an odd duck: variable-word-length decimal, as
| you point out, but targeted at the scientific market -- there
| was even a variant, sold as the 1710, which added extra
| hardware for industrial controls. (The 1401 and its
| successors were the nearly-contemporary low-end business
| models; there are a bunch of differences, but perhaps the
| most significant is that a single 1401 memory location could
| hold a decimal _or alphabetic_ character; the 1620 's memory
| locations were digits, which had to be paired when
| representing characters, making coding for anything involving
| character data a whole lot more awkward.)
| kragen wrote:
| Oh my. I had no idea. Thank you.
| kens wrote:
| Yes, the IBM System/360 was designed to support the full
| 360deg circle of applications (scientific and business),
| which was a rather revolutionary idea at the time.
| kragen wrote:
| Exactly! But in terms of design, there were earlier
| machines that spanned the gap like the astounding Burroughs
| B5000, which was marketed almost entirely to businesses
| (because that was the Burroughs customer base), but with a
| 48-bit word length and floating-point-only arithmetic, and
| including both "numerical" and "character" instruction set
| operating modes. The first delivery was, I think, to NASA.
|
| Also, as Robert points out in
| https://news.ycombinator.com/item?id=30900280, the earlier
| IBM 1620 was similarly ambiguously positioned.
| tenken wrote:
| Why do you reference a year via 01960 or 01940? ... Surely
| you don't mean Hexadecimal... You won't live past 20x0 so why
| the importance?
| krallja wrote:
| Y10K compliance.
|
| https://longnow.org/ideas/02013/12/31/long-now-years-five-
| di...
| allenrb wrote:
| Like aftbit, I also learned about excess-3. It's amazing to see
| what was done to save a few gates back when "a few gates"
| wasn't just a 74-series chip, but an entire handmade board.
|
| But before that, the unidisc blew my mind. I had to do some
| further research and then send to a half-dozen friends before
| finishing Ken's article. Halfway assumed it was a fake photo
| until digging a bit further. Couldn't have looked much more
| like a giant 3.5" floppy if it tried.
| kens wrote:
| Author here if anyone has questions about the board or the Univac
| 1004.
| prashnts wrote:
| Long time reader of your blog, thanks for doing what you do!
|
| So I've been into "connector technologies" (if that's a thing)
| for a while -- more specifically I really admire the simplicity
| of edge connectors that nowadays are basically free (except the
| higher amount of metal than traces, (gold?) plating etc.).
| Anything you'd like to add about these sort of connectors from
| this era? Were they reliable in mating-cycle sense? Could you
| just casually insert them or was there a specific process? Was
| there a standard?
|
| As you can see I don't have a precise question, I'm looking
| more towards the considerations that an engineer at that time
| would have to take into account. Unfortunately it's not very
| easy to google this these days.
| kens wrote:
| The IBM 1401 team analyzed the gold on the SMS card edge
| connectors and found they have 100 microinches of gold, which
| is a lot by modern standards:
| http://ibm-1401.info/SMS_Tabs_IBM_Report_Dec2007.pdf
|
| The connectors were generally reliable; I don't think we've
| had any problems with them. You could clean them with
| isopropyl alcohol if necessary. There was one IBM manual that
| described a process for removing SMS cards where you'd put a
| punch card on either side of the board to protect the board
| against catching on neighboring boards, and then use a
| special puller to remove the board. But we just pull the
| boards out by hand without problems.
| chiph wrote:
| Not about the board, Ken. But I am curious about how you have
| the time to work on projects with the Computer History Museum
| and with Marc on his projects. Seems like you're a very busy
| man. :)
| kens wrote:
| The secret to having enough time is to retire :-)
| Animats wrote:
| Oh, the UNIVAC 1004. Those were often used as peripherals for
| UNIVAC mainframes.
|
| My UNIVAC 1004 story.[1]
|
| [1]
| https://hardware.slashdot.org/comments.pl?sid=957001&cid=249...
| GnarfGnarf wrote:
| I worked for Univac and had occasion to work with the 1001 card
| reader. The 1004 was also popular as a RJE (Remote Job Entry)
| unit and printer attached to the more powerful 1100 series
| computers.
|
| The unit behind the female operator is a row card punch (200
| cards/min.)
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