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Re: Kernel uses only half of Mac IIci memory with built-in video

On Tue, Mar 23, 2021 at 06:50:05PM +1100, Finn Thain wrote:
> Anyway, surely this test for CPU_68020 in Source/mmu_support.c in Penguin 
> is bogus. This must have to do with some quirk of the Mac II logic board 
> and not the type of MMU or CPU.
> So, why sort chunks by address on Mac II? Beats me. I guess I'll have to 
> dig out my Mac II and try EMILE, which doesn't have that hack.

Apparently there was a bug in the original Mac II ROM that couldn't
handle more than 4MB in bank A. That would mean that anyone who had
more than 8MB had the larger modules in bank B. The claim online is
that it is possible to replace the ROM chips with a fixed version
(which happens to be the part also found in a Mac IIx) to enable
using larger modules in both banks. It was also supported to replace
the IWM chip with a SWIM chip as long as you had also replaced the
ROM chips with the newer ones. In any case, both the II and IIx need
some funny PAL enhanced SIMMs to use larger sizes. They fixed that
in the IIcx and SE/30, which are the same basic logical design.

However, I would have thought this would lead to the opposite solution.

	Brad Boyer

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