Re: PCbox, an add to the MS-DOS 1.25 project

Den Tue, 17 Oct 2017 08:37:33 +0100 skrev smf <smf@null.net>:
> On 17/10/2017 05:01, Mia Magnusson wrote:
> 
> > That is also the reason for
> > the Z80 being so slow in C128 compared to other Z80 implementations.
> 
> Other Z80 implementations have the same problem when accessing video 
> memory and the screen is being drawn, you're right that the C128
> suffers because there is only video memory. But also because there
> wasn't time/money to make the VIC2e perform bus arbitration properly.

Yes, since CP/M on a 40 column display isn't much fun it would had been
better if the VIC-II were switched off completely from the bus and
giving the Z80 complete control of the bus.

> With an 8088 it would certainly make sense to add more ram which it
> has faster access to and let the 6502 access it through a paging
> mechanism.

It would be nice if we had some modern programmable logic replacement
for the C128 MMU (and whatever more IC's that does the job that the PLA
does in a C64). That would open up for various add-ons.

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