CP/M

From: Jack Peacock <peacock_at_simconv.com>
Date: Fri Jun 12 20:11:00 1998

> But I was reading the CP/M manual (pretty shallow), and it mentions a
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
Received on Fri Jun 12 1998 - 20:11:00 BST