Hi Ole & Ben,
Regarding memory limitations for the Z80 and CP/M:
The Z80 has a 16-bit address bus, therefore a total
memory space of 64K max. Using a technique called
paged memory (or "bank switching") it is possible
to swap 4K or 16K (or even 32K) banks so as to
access as much memory as you can wire in.
The CPU (and therefore the O/S) are, however,
limited to 64K of directly addressed memory.
Disk space is, of course, another matter.
All you had to do was customize the BIOS code
to change the disk blocking routines to access
larger disks. I never saw anyone go larger
than 40MB on a CP/M hard disk though.
(An interesting side note: one of the reasons
you can get much more out of 64K on a Z80 than
on an 80x86 processor is that the instructions
for the Z80 are shorter and take fewer processor
states (T-states) to execute, so a 4MHZ Z80
runs instructions as fast as a 6 or 8MHZ 8086.)
Regards,
Garry
[EMAIL PROTECTED]
[EMAIL PROTECTED]
-----------------------
Ole Juul wrote:
>
> Hi Ben,
>
> You wrote:
> > oj>64k RAM which is as much as the operating system can
> > oj>handle.
> > Are you sure? I've had more than that with CP/M 2 -
> > but not on a Z80 machine.
>
> Actually, now that you mention it, no I'm not sure. <g>
> The machine (KAYPRO II) comes with 64k, but now that I
> check the docs, it is not clear to me exactly how much
> memory the OS can handle. It says that it will access 16
> drives with up to 8Meg files each, and that they plan
> expandability to 32Megs. Perhaps then, the address space
> is 128Megs? I'm not sure if that relates to addressable
> ram though. The Z80 may have it's own limitations too.
>
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