6 Nov
2012
6 Nov
'12
10:31 a.m.
On 11/06/2012 12:34 PM, Ethan Dicks wrote:
CP/M is a file system and the abstracted IO is in the
BIOS, why not add
to the bios a taskmanager that has an interrupt driven tasklist to run
multiple CP/M spaces sharing the bios and BDOS(filesystem).
Nothing says you cannot.
Therein lies
the problem. CP/M80 was single user. CP/M+ or MPM
added the multitask layer with what we call legacy compatibility
(single 64K page mapping). IF DOS/8088 did not enter when it did
then where we might have gone is still open.
On Tue, Nov 6, 2012 at 12:18 PM, Allison <ajp166 at
verizon.net> wrote:
That should have been Z280 MMU not Z180. Between the two there
is night and day for MMU ops in structure and programming.
The Z280 does a scatter gather map like PDP11 MMU and the Z180
does a start page end page mapping.
On 11/06/2012 10:53 AM, Ethan Dicks wrote:
OK. That's what I thought from my limited understanding of
CP/M, but
I do appreciate the well-educated response.
...what CP/M software is out
there (except maybe a RAM disk) that can *use* 1MB?
Essentially none at the
applcation level. It does make a super fast ramdisk though. For
aps that did overlays
like multiplan or multipass assemblers or compilers that is a huge speedup.
Sure.
I've done that with a KT8A, 128K and a PDP-8... Lots of
address-constrained systems have benefited from falling RAM prices by
loading up 4x (or more) on the amount of RAM that user programs can
see but that is still usable behind system calls/device driver access.
...Things like tassk switching are possible
Makes sense especially if you might want to, say, keep an editor
session alive and switch over to something else (like a compiler) and
back.
The Z180 MMU is near identical to the PDP11
MMU save for the bits for page protection and memory exception traps.
Interesting.
I had no idea. I've done some very minor fiddling with
the PDP-11 MMU under RT-11 (IIRC it involved some odd mapping twiddles
with a 512x512 framebuffer card and a scatter-gather DMA engine). At the extreme
there is Uziunix that uses 32K of ram and maps applications
to 32k pages up to whats available. Since unix (even uzi) is a multitasking
system tasks loaded in remote pages get their timeslice and can communicate
with other tasks or applications.
Sure. I get how someone might use 1MB on an
8-bitter with a
pre-emptive multitasking system, but that's not what I think of when I
think of CP/M 2.2 on a Z-80. In short
anything a PDP-11 with MMU can do. (its a 16bit address machine
too).
If one is developing code, I do see numerous possibilities. I was
more curious about being strictly a user and soaking up that much RAM
outside of turning it into a RAM disk. It's not that I would never
develop any code on CP/M, but it's far more likely I'd be grabbing
stuff off the Walnut Creek CD-ROM or downloading things to run on it. Thanks for the excellent reply.
CP/M is still
useful and z180s are availeble to beyond 20mhz
imagine a 20 or 33mhz Kaypro..
Allison
-ethan