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From: lsalomo@hubcap.clemson.edu (lsalomo)
Newsgroups: comp.os.msdos.programmer
Subject: Re: .com and .exe files
Message-ID: <11349@hubcap.clemson.edu>
Date: 2 Nov 90 13:26:38 GMT
References: <92.2730D05F@bohemia.UUCP>
Organization: Clemson University, Clemson, SC
Lines: 21

From article <92.2730D05F@bohemia.UUCP>, by Greg.Smith@bohemia.UUCP (Greg Smith):
> The extensions of the files are mainly there for our referance.  The way the 
> computer differentiates (sp) between the files is the header at the 
> beginning of the file.  on EXE's  an  "MZ" will be the first two bytes in 
> the file, while com files start out with actual code.  Also, following the 
> MZ is a Program Segment Prefix(PSP) which defines many other needs, and 
> memory/stack useage terms.

Not meaning to start a big discussion, but following the .EXE id ('MZ' as
you pointed out) is a header (NOT THE PSP) which describes the size of the
code in pages, the entry point, etc. plus the relocation table which the
loader uses to do any segment fixups before jumping to the entry point.

Cheers,
Q - the "Q"uestor for knowledge (, a degree, etc.)

lsalomo@hubcap.clemson.edu
ibmman@clemson.clemson.edu
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