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United Kingdom Hardware Build

EDSAC Diagrams Rediscovered 37

mikejuk (1801200) writes Due to its importance in the history of computing, the UK's Computer Conservation Society embarked on a 4-year project to build a replica of EDSAC. The main challenge facing the team of volunteers who are working on the rebuild is the lack of documentation. There are almost no original design documents remaining so the rebuild volunteers have to scrutinize photographs to puzzle out which bits go where. However, three years into the project, a set of 19 detailed circuit diagrams have come to light and been handed to the EDSAC team by John Loker, a former engineer in the University of Cambridge Mathematical Laboratory. "I started work as an engineer in the Maths Lab in 1959 just after EDSAC had been decommissioned. In a corridor there was a lot of stuff piled up ready to be thrown away, but amongst it I spotted a roll of circuit diagrams for EDSAC. I'm a collector, so I couldn't resist the urge to rescue them. " In the main, the documents confirm that the team has been correct in most of its re-engineering assumptions, but the drawings have thrown up a few surprises. The most significant discrepancy between the original and the reconstruction that the papers reveal is in the "initial orders" (boot ROM in modern terminology). In the absence of fuller information, the reconstruction team had considered and rejected one possibility which was in fact the one that was used by the original engineers. That will now be rectified in the reconstruction, which is due for completion in late 2015.
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EDSAC Diagrams Rediscovered

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  • by UnknownSoldier ( 67820 ) on Sunday June 29, 2014 @02:58PM (#47345763)

    Always funny to read about a geek seeing the value in saving something for "historical sake" while a company / university just wants get rid of old "junk"

    One man's treasure is another mans junk.

    Will interesting to see if the completed project actually works.

  • by AbrasiveCat ( 999190 ) on Sunday June 29, 2014 @04:56PM (#47346221)
    So the they get a few prints of part of the circuits, 9 pages of 150, and they see they made mistakes replicating the original. I wonder how many other mistakes they have made, and what happens if they are finishing and some more drawings surface showing they got stuff wrong? Will they throw it out the wrong and make it as designed or just say "hey good enough, we got most of it right"?
    • and what happens if they are finishing and some more drawings surface showing they got stuff wrong?

      I imagine that they will revise anything that seems to explain a problem they've been having, or answers a question they couldn't otherwise answer. My question was along the avove lines, though. What if there have been changes since those drawings, for which there is no documentation? Heck, they might even undo something they did right. I imagine they're going to take that possibility into account, though. If they were idiots, this probably wouldn't seem interesting.

    • That was my thought too... Nineteen pages of the size shown in the pictures is pretty much nothing compared to a complete set of diagrams. It's like getting nineteen pages out of Game of Thrones (which is itself just one volume of a much larger series). If they found errors with so little new information, it does not give me much confidence that their recreation is accurate to any great degree. (Especially given that they tossed out an approach now known to be the one used.)

  • by cstacy ( 534252 ) on Sunday June 29, 2014 @07:36PM (#47346865)

    Since microelectronics, people don't re-wire CPUs anymore...well, they do if it's FPGAs and such. But even in the late 1960s computers were constructed with discrete electronic parts on PCBs. We got a lot of milage out of those vintage machines. I remember hooking up a primitive (by today's standards) logic analyzer to trace signals through the CPU, replacing components such as pulse amplifiers and flip-flops that comprised machine registers. In a research lab setting, it was not uncommon to modify the machines -- for example, new circuits to support dynamic paging (memory bus modifications, associative memory tables, etc.) So I am sure the working EDSAC machine must have had modifications that were not even recorded on these diagrams they have recovered. The story reminds me of a logbook entry that another hacker wrote when repairing the PDP-6 at the MIT AI Lab around 1982. It simply read, "Found wiring here not on schematic. Repaired circuit."

  • Either to the National Museum of Computing (UK) or the Computer History Museum (US), and scan them so they can be put online.