4 ms·
IBM's computers of the 1960s had wirewrapped backplanes and they were reliable. (The Xerox Alto and Apollo Guidance Computer are two other systems with wirewrap
by kens 4y ago
IBM's computers of the 1960s had wirewrapped backplanes and they were reliable. (The Xerox Alto and Apollo Guidance Computer are two other systems with wirewrapped backplanes.) I don't think we've ever had a backplane problem with the IBM 1401 at the Computer History Museum. IBM did a lot of field changes to the wirewrapped backplane, either to fix bugs or add new features. They had a specific process to go through. You couldn't just cut a wire; you had to unwrap the wire and remove it. But there could be up to 3 layers of wirewrap on one pin, so in worst case you had to remove 2 wires before you could get to the wire you actually wanted to remove. After you replaced the wire you wanted to replace, you'd need to replace the wires you removed to get to that wire.
- greenbit 4y agoAnd hopefully the other ends of those two were top-most, so it could end there. If not, there could be even further collateral rework.
- anyfoo 4y agoRepresent that network of wires as a directed graph. Find the biggest tree spanned within the graph. This will be the wire that, should you ever have to replace it, will have you cancel all your other plans for some foreseeable time…
- kens 4y agoYes, I think it was a requirement that both ends of a wire were at the same level on the pin. So you might have an additional top-level wire but you wouldn't end up with a long dependency chain. I should also mention that the original (non-field) wire wrapping was done with an automated machine, the Gardner-Denver Automatic Wire-Wrap Machine. It had X-Y carriages with wire-wrap tools and it wire-wrapped the backplane according to a deck of punch cards. Details: http://www.bitsavers.org/pdf/gardnerDenver/SM506753_Parameters_for_Programming_the_Gardner-Denver_Automatic_Wire-Wrap_Machine.pdf http://www.bitsavers.org/pdf/gardnerDenver/SM506753_Paramete...