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Reverse-Engineering a Mysterious Univac Computer Board

posted by Fnord666 on Tuesday April 05 2022, @08:34PM   Printer-friendly
Hardware

owl writes:

http://www.righto.com/2022/04/reverse-engineering-mysterious-univac.html

The IBM 1401 team at the Computer History Museum accumulates a lot of mystery components from donations and other sources. While going through a box, we came across the unusual circuit board below. At first, it looked like an IBM SMS (Standard Modular System) card, the building block of IBM's computers of the late 1950s and early 1960s. However, this board is larger, has double-sided wiring, the connector is different, and the labeling is different.

I asked around about the board and Robert Garner identified it as from the Univac 1004, a plugboard-controlled data processing system from 1963. The Univac 1004 was marketed as a "Card Processor" rather than a computer, designed for business applications that read punch cards and producing output, but still required calculation and logical decisions. Typical applications were payroll, inventory, billing, or accounting.

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  • (Score: 4, Interesting) by Anonymous Coward on Tuesday April 05 2022, @09:08PM (2 children)

    by Anonymous Coward on Tuesday April 05 2022, @09:08PM (#1235082)

    Interesting blog post, and great stuff in the notes at the end that I found really interesting, such as:

    To reverse-engineer the board, I took photos of both sides, flipped the image of the back in GIMP so the two sides were aligned visually, arranged the components on a schematic in EAGLE, and connected the components to match the circuit board. Then I moved the components around until the layout made sense.

    and

    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.

    • (Score: 2, Funny) by Anonymous Coward on Tuesday April 05 2022, @11:32PM

      by Anonymous Coward on Tuesday April 05 2022, @11:32PM (#1235125)

      amazing! not a 100 years have past and we already got computer archeology!

    • (Score: 2, Funny) by anubi on Wednesday April 06 2022, @10:22AM

      by anubi (2828) on Wednesday April 06 2022, @10:22AM (#1235192) Journal

      I am quite impressed by the use of Eagle and Gimp.

      Looks much easier than how I been doing it.

      Not only that, your output is already in Eagle when you're done.

      Me, my output is a really crude pencil drawing on sometimes several pieces of paper.

      Gee, what I have been doing is just about as archaic as that UNIVAC board.

      --
      "Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]

  • (Score: 0) by Anonymous Coward on Wednesday April 06 2022, @12:28AM (1 child)

    by Anonymous Coward on Wednesday April 06 2022, @12:28AM (#1235133)

    Didn't Sperry merge with Univac? What happened then?

    Univac name still survives as HVAC control module producer. At least it did - my home thermostat module is branded Univac.

    • (Score: 4, Interesting) by owl on Wednesday April 06 2022, @01:10PM

      by owl (15206) Subscriber Badge on Wednesday April 06 2022, @01:10PM (#1235209)

      You are confusing Univac with Unisys.

      Sperry and Burroughs merged to become Unisys (the company).

      Univac was a different company that was bought by Burroughs some time prior to the Sperry/Burroughs merger into Unisys.

  • (Score: 3, Interesting) by Mojibake Tengu on Wednesday April 06 2022, @03:10PM

    by Mojibake Tengu (8598) on Wednesday April 06 2022, @03:10PM (#1235247) Journal

    I observed very similar DTL logic boards while I witnessed decommissioning already obsolete Siemens 2000 mainframe in 1978, which was being replaced by Soviet EC-1040 mainframe (TTL logic based) at that time.

    Got some of these, perfect source of germanium diodes and transistors for a couple of next years to me.

    Though other Univac mainframes I worked on in 80's were all TTL as well. But the style of much bigger boards with their coordination system was the pretty same as pictured in TFA. Those boards were very easy to fix manually by soldering, thanks to their schematic documentation which included coordinates of the components.

    --
    The edge of 太玄 cannot be defined, for it is beyond every aspect of design
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