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Re: Multi-Tasking on Apple IIgs?



David Wilson wrote:
The Wizard of Oz <wizard@emeraldcity.gov> writes:

	I was going to ignore this thread until I thought about the possibility
of co-processor cards. If a co-processor card could be active the same
time as the GS processor then you could get true multi-tasking as opposed
to the time slice mechanism everyone else is suggesting.


It depends on the type of co-processor card. A Stellation Mill with a
6809E chip can run a program while the motherboard CPU runs another program
but as both are using the same RAM on the motherboard they still time slice
(just at a much finer level than an interrupt driven pre-emptive multitasking
system) with the 6502 only running during cycles when the 6809E does not need
to use the data bus.

Do any co-processor cards for the Apple II family have on-board RAM allowing
them to run completely independently of the motherboard (apart from I/O)?

Yes, the PCPI Applicard (aka MicroPro StarCard), Microsoft Premium SoftCard IIe, ALS CP/M-3 card and many others had their own RAM. That said, the only activity which actually leveraged the concurrency was motherboard print spooling. Everything else involved a synchronous handshake of one sort or another.