To: opendos AT delorie DOT com
Date: Fri, 16 Feb 2001 02:34:50 5
Subject: Re: CP/M Question
Message-ID: <20010216.024044.-4038533.0.editor@juno.com>
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From: Bruce Morgen <editor AT juno DOT com>
Reply-To: opendos AT delorie DOT com


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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