please see imbedded comments below. Dick -----Original Message----- From: allisonp(a)world.std.com <allisonp(a)world.std.com> To: Discussion re-collecting of classic computers <classiccmp(a)u.washington.edu> Date: Friday, April 09, 1999 7:18 AM Subject: Re: stepping machanism of Apple Disk ][ drive (was Re: Heatkit 51/4 floppies) It was, indeed, but not when the Apple was designed, since the 6845 and 6545 didn't yet exist. of it vindicated There were many people who disagreed with that performance comparison. The two processors (I used them both extensively) were different enough that comparison and contrast was not easy. The Z-80 had many registers and a rich instruction set of which much was awkward and difficult to use. The 6502 had fewer registers and fewer instructions but they were amplified by addressing modes not readily available to the Z-80 user, particularly if his code was for CP/M which sort-of required you stick to the 8080-compatible instruction subset. The fastest 6502 available in 1980 was a 4 MHz processor which stroked memory for 125 ns almost every cycle in its typical application. The Z-80 had just that year become available in a "B" version (6 MHz) which stroked memory for slightly less than 3 clock ticks on a memory cycle and barely 1 (166 ns) on an unmodified M1 cycle. Having said that, and given (1) that the two processors executed code at about the same rate for the same memory cycle length (hard to prove or disprove) and (2) memory cost was more of an issue than system performance, hence the memory cost was used to set the rate at which the CPU operated, I'd say there's really no basis for comparing the actual performance of the two processors. The TRS-80 could have been put out with (1) an 80x24 display rather than the 16x64, it could have solidly supported double-density FD's (in the model 3) and it could have operated at about 4MHz rather than the 2.-something it used, and it could have switched in and out the ROM so it could run CP/M but for the greed of Tandy Corp. It would have cost them an additional $5 and change to put those features in their model 3, but they thought "well, we're going to sell a million of these . . . " and decided they preferred having the dollars. Had they gone the other way, they probably would have had the "personal computer" market all to themselves. They had a huge distribution network, a huge sales force, a huge service network, unlike any other microcomputer manufacturer of the time. Within a year, Apple owned the personal computer market, particularly with respect to businesses, even though Radio Shack had better packaging by the time the Model 3 came out. That was also about the time it became common to see the 80x24 displays, the 8"disk drives, the nearly 4MHz Z-80 running CP/M, the extra 16K memory, etc. on the Apple II. If Tandy had gone with the better design, which was on the table, there probably would be no IBM PC today.