multiple cpu machines Re: rogues galleries

Jules Richardson julesrichardsonuk at
Tue Nov 28 15:43:50 CST 2006

Chris M wrote:
[Dimension 68000]
>  Was curious if there was anything like it across the
> pond. Or did I ask this already...

Closest thing is probably the humble BBC micro, to be honest. Acorn designed 
them from the outset to allow add-on processors to be used (externally on the 
model B, and either externally or internally with the later Master series), 
and for the second processor to be able to take over control of the host BBC. 
They always had plans for Z80 and additional 6502 boards for the machines; I 
believe that the 32016 and 80186 boards weren't envisaged until later on.

Several manufacturers (including Acorn) made coprocessor boards for the 
machines (notional OS in brackets, although you were free to run what you 
wanted really):

Acorn Z80 (CP/M)
Acorn 6502 (application-level code)
Acorn 65C102 (application-level code)
Acorn 32016  (Master internal, PanOS)
Acorn 32016 (1MB variant, PanOS)
Acorn 32016 (4MB variant, PanOS)
Acorn 80186 (DOS)
Acorn 80286 (DOS)
Acorn ARM1 (Brazil monitor only)
Acorn A500 (Arthur. Not to be confused with the A500 distinct machine)
Casper 68000 (FLEX / program development)
Cumana 68008 (OS-9)
PEDL Z80 (unknown)
Torch Z80  (CP/N)
Torch 8086 (DOS)
Torch 68000 / Z80 combo (UNIX and CP/N)

Two versions of the Torch 68k board existed - the later one was faster and 
with more on-board memory. Two versions of their Z80-only board existed too; 
one had a local serial interface.

People have privately homebrewed other CPUs for the system (6509, 6809, ARM7 
and PDP-11 spring to mind).

However, whether all this 'counts' or not is debatable; Acorn didn't (sadly) 
forsee people wanting to have more than one 'secondary' CPU attached at any 
one time, so the connection between the BBC side and any additional CPU was 
really point-to-point only rather than a true bus; I think Torch were the only 
people to offer a setup that contained both 68k and Z80 alongside the BBC's 
native CPU (I seem to recall that in their case the switch between CPUs is 
handled by on-board firmware and a bit of voodoo)



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