On Fri, 11 Aug 2006 12:01:13 -0700, "Chuck Guzis" <cclist at sydex.com> wrote: IIRC the PDP 9 (and possibly the 5 and 7) were async machines. That was my first "personal" computer (nobody else wanted to touch it...) and I spent many hour programming and keeping the beast running. When the thing failed it was a real pain to troubleshoot. You would find a signal on the backplane that was out of spec, but when you put the card on the extension board to troubleshoot the damn thing would start working. That and the unique control "memory" that would stop working when things got damp... CRC