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From: Georg <dosusb AT googlemail DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: System()
Date: Sun, 6 May 2012 13:54:54 -0700 (PDT)
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To: djgpp AT delorie DOT com
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When I open a DOS window in Windows XP, mem.exe tells me that 590 kb
are available for a program.

Now I made the following program:

#include <stdio.h>
main(int argc,char **argv)
{
system("mem.exe /d >memn.tmp");
}

1. Windows XP:
When I run this on Windows XP it tells me that 572 kb are available
for a program.
There are two command.com programs loaded with 2976 bytes each, plus
the above program which I called testsys.exe which consumes 16.540
bytes and has 1936 bytes data.

2. Real mode DOS 7.0:
When I run this program in real mode with DOS 7.0 it tells me that 366
kb are available for a program.
There is one command.com with 6k and one command.com with 88k. 43k for
CWSDPMI. The above program still is 16k but has 162k(!) data this
time.

So a rough calculation: 572k minus 43k for CWSDPMI and minus 162k for
testsys.exe's data gives 367k remaining. That is what DOS tells to be
available for a program.

Question:
Maybe one can load high CWSDPMI. But why are there 162k for
testsys.exe's data while it is just 1936 bytes in Windows XP?

I use gcc 4.5.3.

Thank you for the links Rugxulo. I looked at ytree: it uses system()
to execute a program. Since ytree is mainly developed for Linux this
does not result in any memory problems.

As far as I could find, DOSZIP uses int21/ah=4Bh to execute a program.
I guess this the assembler equivalent for system().

Georg