CP/M

16-user capability and password protection. How does this work and how secure is it? Also, would you say that the Z-80 was better than the 8088? It was certainly used much more... The "16 user" isn't really a multi-user capability. Unlike MS-DOS, Unix, VMS, etc., CP/M did not have subdirectories. The main directory was it, everything fit there. This was not so convenient, so "user areas" came into being with CP/M v2. The 16 users are actually numbered subdirectories. The "C> USER 5" command would switch you to subdirectory 5, equivalent to a "C> CD \DIR5" in DOS. The idea was if multiple people used the machine, each would have their own area. On V3 the user 0 area was a common directory, I think there were some commands to control this (very rusty on CP/M V3). I don't think CP/M V3 was ever implemented on the Apple card, since V3 was designed to use banked memory over 64K. As for 8088 vs. Z80, I would rate the 8088 as one step above the Z80. It was slower, but had a larger instruction set and a crude MMU built in, out to the 1MB limit so familiar today. The Z80 was a bit faster at the same clock rate, and the 8088 never got to a very high speed, IIRC it got to about 8 or 10Mhz in the Intel version, NEC sold variants out to 12Mhz. The Z80H was an 8Mhz part, it kept up with the 4.77Mhz original IBM quite well, except for the memory limitation. BTW, on S-100 systems the 8086 was far more common than the 8088, since the S-100 could support a real 16-bit bus. Zilog and Hitachi eventually extended the Z80 out to 512K and then 1MB with an MMU too, but it was never as flexible as the segment registers in the 8088. As far as design difficulty, using an 8088 or Z80 was about equal. The 8088 had a minimal mode for small designs, or support chipset for expanded systems. The Z80 took some random logic for the clock signal and needed some type of MMU if you needed more than 64K. Jack Peacock