Nobody really cares, but it's certainly not reasonable to argue that, because it has a Z in it's name, the Z180 or Z280, or whatever, is a Z80. I once involved myself in a pretty thorough evaluation of 6502 and Z80 and found that it's difficult as hell to conjure up a test that really compares the two on a strict basis of performance. Most manufacturers essentially rated their processors on the basis of how many NOP's they could execute in a second. It seems silly, but it's probably as good a yardstick as any for establishing relative speed. However, that definitely gives the 6502 an advantage, and we wouldn't want to disadvantage the venerable old Z80, since everybody knows it's faster than the 6502, right? Anybody who gives this comparison any thought will quickly realize that it's not an easy pair to compare. In reality, there was a MUCH larger software base for the Z80, so many tasks would still be waiting to be coded, even today, but for the fact that they'd already been done for the 8080, the code for which runs without modification, in most cases, on a Z80,.by the time the 6502 became popular. Now, I've always believed the 6502 at 1 MHz to compare favorably with the 4 MHz Z80, but I used the Z80 running CP/M 2.2 to do useful work, since it was a lot more trouble squeezing useful work out of a 6502 back in '78-'79. Dick ----- Original Message ----- From: <CLeyson(a)aol.com> To: <classiccmp(a)classiccmp.org> Sent: Friday, December 21, 2001 5:34 PM Subject: Re: 6502/Z80 speed comparison (was MITS 2SIO serial chip?)