6 Nov
2012
6 Nov
'12
9:18 a.m.
On 11/06/2012 10:53 AM, Ethan Dicks wrote:
Hi, All,
I'm not joining in the kickstarter because I already have a P112 I
purchased as a bare PCB and loose SMD parts in the previous round. I
just uncovered it last night moving some things around and started
tossing build-parts into a bin to put it together. I do happen to
have a couple of 32-pin JEDEC 512K SRAMs (originally for an SBC6120
RAM disk PCB that got destroyed in the mail), so I _can_ fully
populate it, but it got me wondering... what CP/M software is out
there (except maybe a RAM disk) that can *use* 1MB?
Essentially none at the applcation level. The MPM and CPM+ OSs can map
ram for
processes that are resident. but the system still views ram
as a 64K with page switching/mapping.
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.
Even with vanilla CP/M-80 (V2.x) it's possible to map the added ram as
buffers for
keyboard IO (circular buffers for interrupt io), BIOS itself can be in a
new page
(up to 64K) with all maner of extended features like large buffers
without the
high cost to the TPA. Things like tassk switching are possible where a
sleeping
app is loaded in a remote page and by keyboard command brought into
action for
use (handyman for the kaypro does this save for its in eprom in mapped
space).
I did do a S100 system that carried it to extremes (still CP/M-80) with
mapped ram
and multiple CPUs sharing common and private mapped space with a task
manager
overlay to get functional multitasking. Later I got a few Z280s and
that part
has a differnt MMU than the Z180. The Z180 MMU is near identical to the
PDP11
MMU save for the bits for page protection and memory exception traps.
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.
All this is done using Z180 (P112) that has a 1MB address mapping system.
I have a bit of experience with 48K-64K CP/M machines (mostly Kaypro,
but some others), because back when I was using it, that was how much
memory 8-bitters had. I didn't mess with them much after 1985, so if
there was still any development on that platform, I didn't see it.
So why *does* the P112 have 1MB of RAM? What's the space over 64K good for?
Cheers,
-ethan
In short anything a PDP-11 with MMU can do. (its a 16bit address
machine too).
See above..^ ;)
Allison