More thoughts on building a Z-80 (64bit!!!)

From: Allison J Parent <allisonp_at_world.std.com>
Date: Fri Oct 23 22:18:01 1998

< Are z80's still being produced?

Yes.

<If so, are they the same as the 1980 ones?

actually the z80 is 1976 design and yes. The z180 is an enhanced part
that is very popular in controls and other embedded uses.


<I would think so, since the TI-86 (still in production) uses
< a z80. BTW, I guess comparing the multi-Z80 system to a 386 isn't too
< fair.

It's fair as the z80s were only running at 6MHz.

<How much faster is it than 1 z80 running the same program?

Not terribly. The actual test only used one. The rest were doing
background tasks (printing). Z80 excels at IO and byte oriented tasks.
The real advanatge was the system had highly optimized IO channels for
everything and the disks had track caching. The other minor advantage is
the z80 code used was tight and by time 386s got in PCs code bloat had
already set in.

FYI: the machine was originally designed to tackle several things more
speed from a cpu, Multiprocessing/multitasking and more efficient IO
systems. The IO systems part proved to be the key to using one cpu more
efficiently. Multiple CPUs had a minor advantage that was offset by
fairly complex programming. To this day that system runs but with only
one master cpu installed(the other three are spares).

Two years later Compupro would come up with the MPX1 combined with
their frequent use of DMA to make one of the fastest s100 systems
available (for any given cpu). Basically doing the same work I did
earlier for myself and proving that multiple CPUs and DMA can be a
performance enhancement when applied to the bottlenecks (most tend to
occur at the IO level).

<Why is everyone making multi-z80 machines, anyway?

Partially to capitalize on available software (mountains of it all free)
and experince.

<Why not 6502 or 6800 or even (gasp!) 8088?

Because those were done also. I have a trackstar128, two 6502s. IT
has a lot to do with the way the CPUs interface and the ability to
interconnect them so they don't fight each other. The 8088 has a
selection of bus interface chips that allow for multiple CPUs on the
same buss (8289). Also multiple CPUs are a cost/complexity vs
performance race and some win better in that contest.

Allison
Received on Fri Oct 23 1998 - 22:18:01 BST