Mail Archives: opendos/2001/02/15/21:45:31
On Fri, 16 Feb 2001 12:43:59 +1100 "da Silva, Joe"
<Joe DOT daSilva AT emailmetering DOT com> writes:
> I hope a question about DR-DOS' predecessor is not too
> "out of place" here ... ? <g>.
>
> Anyway, I have read information about CP/M 1.4 and
> 2.2 (or was that 2.0?) that said the command processor
> (CCP) occupies 2K of memory ...
>
> Now, my question is this : Were there any versions of
> CP/M (or CP/M clones), in which the command processor
> (CCP) was larger than 2K?
CP/M v3.x, aka CP/M+, had a
larger CCP implemented as a
disk file, just like CP/M-86
and DOS. Hal Bower's fancy
version of Z-System also has
no fixed CCP size limitation.
>
> BTW, the recent question about "total memory" is what
> has reminded me to ask about this, because, as far as
> I can tell, the only way to work out how much memory is
> available/free on a CP/M system, is to subtract the CCP
> size from the BDOS starting address ...
>
Actually, you just use the
BDOS call vector at 0005h
and round down to the
closest page boundary --
that's as high in RAM as you
can write to without
impinging on BDOS -- as long
as you terminate your program
with a warm boot (e.g. CALL 0
or RST 0), you can safely
overwrite the CCP's address
space because that warm boot
will reload the CCP from
disk and then jump to it.
You only have to subtract the
CCP size if you plan to use
or restore the CCP stack and
end the program with a RET
instruction instead of a warm
boot.
> Joe.
>
>
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