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Comment: Documentation vs. Implementation (Score 4, Interesting) 37

by cstacy (#47346865) Attached to: EDSAC Diagrams Rediscovered

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."

Bus error -- please leave by the rear door.

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