On Sep 30, 19:12, ajp166 wrote: Ah, then you'll know what the difference(s) was/were. While looking up 8080A and 8080 (except all my 1976 and 1979 Intel Data Books say is that they're functionally and electrically compatible) I discovered that NEC made two versions, both called 8080A, but one with some enhancements. I assume that this was rather like the idea they used in the V20. The note said that 8080A's from authorised second-sources were competely code compatible but the enhanced NEC version was not, and wouldn't always run certain Intel code. What was the difference, and what made it not run certain programs? -- Pete Peter Turnbull Network Manager University of York