multiple cpu machines Re: rogues galleries

From: Jules Richardson <julesrichardsonuk at yahoo.co.uk> Chris M wrote: [Dimension 68000] 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) cheers Jules