Quote: Sometime after Bill pulled out of Harvard, a computer program listing turned up behind an old file cabinet. It was printed on 11x17" paper on the old, all-caps line printer that was hooked up to the PDP-10. As is well known, that BASIC interpreter had been written on the PDP-10. It was cross-assembled, which means that unused PDP-10 op codes had been given the names of the 8080 instructions, and when the PDP-10 tried to execute these instructions a "trap" occurred. In the trap code the programmers had added some emulation routines to make the PDP-10 do what the 8080 would have done if it had been executing the instruction. This made it possible to use the PDP-10 debugging tools to debug the 8080 code. Indeed, legend has it that they never saw an actual 8080 chip the whole time they were debugging the interpreter. Pretty clever bootstrapping exercise. |