The PDP-11 bus is really simple, it's easy to whip up custom cards with a handful of TTL chips. Also DEC used to sell all the parts separately, including backpl

The PDP-11 bus is really simple, it's easy to whip up custom cards with a handful of TTL chips. Also DEC used to sell all the parts separately, including backplanes which had a wirewrap pin on every contact. As a result, integrating a PDP-11 (more usually LSI-11 on QBus) into a system was quite simple - bolt a backplane to the end of a 19" rack of DIN41612 connectors and wirewrap the two together (we did systems with 10 or more motor control cards, each with around 100 TTL chips on). A particularly nice feature of the bus is that it was memory-mapped, and everything (memory as well as custom hardware) would send an ACK signal back to the processor when addressed; addressing a non-existent memory location would cause a bus trap. Edit: The bus is simple enough that creating an arduino, say, interface to drive old DEC cards woould not be hard. I'll keep that thought for the next time someone needs their nuclear power station updating [0]. [0] https://news.ycombinator.com/item?id=5904191 https://news.ycombinator.com/item?id=5904191