Date   : Tue, 20 Nov 1990 21:29:04 GMT
From   : comp.vuw.ac.nz!actrix!ewen@uunet.uu.net (Ewen McNeill)
Subject: Amstrad CPC -- HDs

In article <1990Nov19.090518.3479@simasd.uucp> donm@pnet07.cts.com (Don
Maslin) writes:
> ewen@actrix.co.nz (Ewen McNeill) writes:
> >In article <5543@uafhp.uark.edu> bbs00167@uafcseg.uucp (Keefe Jackson)
writes:
> >> 
> >> Does anyone know anything about the Amstrad "128k CP/M" machine? 
> >> Is there a hard disk available for it? Is it still availble?
> >
> >I know a reasonable amount about the Amstrad CPC6128 (which I presume
> >[...] 
> >There is not a hard disc available for the 6128, to my knowledge.
> 
> Assuming that it is a Z-80 based machine (display of ignorance here!), it
> seems that it might be possible to get a HD kit from Emerald Microware which
> uses a small daughter board that plugs into the Z-80 socket plus the
WD1002-05
> hard disk controller.  The one problem that might crop up would be the
> software modifications to the BIOS.  I know Emerald has it for 2.2, but I'm
> not sure about 3.0.  A telephone call should answer that though.
> 
> Ewen, would you care to comment?
Certainly, I will comment :-)
 
The machine is definately Z80 based, so your solution might well
work.  Software modifications of the BIOS could be difficult, as
could be keeping up with the speed of a HD.  The machine runs at
4Mhz with one wait state (effective speed is said to be 3.3Mhz).
The machine does not support DMA, or Interupt driven Disk IO (the
floppy IO is done by polling the controller as is the serial IO --
both _cannot_ be done at the same time :-) 
 
I think the answer is that technically it might be possible, but
the only real way to approach the problem (from my point of view)
would be to build a seperate (Z80 controlled) Disk drive manager
(supporting Floppies and HDs).  That would allow an implementation
of DMA - and with big enough cache, reasonable amounts to be read at
one time.
 
Again, BIOS would be a problem.  I don't have source to it (though,
I may well reverse-engineer it one day :-) and the CPM 2.2
implementation on the Amstrad only allows for 42K TPA.  (The screen
on this machine is a graphics only one -- and it takes 16K!).
Amstrads are definately cut price machines.  One possible solution
(with expanded memory (of which I have 512K!)) might be to run CP/M
in a different bank from the screen.  Still, someone would have to
do a lot of work.
 
One final problem -- the HD would still cost more than the machine
:-)

-- 
Ewen McNeill.                          Email: ewen@actrix.gen.nz