Date: Thu, 26 Oct 1995 16:15:10 +0300
From: "Alexander V. Lukyanov" <lav AT yars DOT free DOT net>
To: A DOT APPLEYARD AT fs2 DOT mt DOT umist DOT ac DOT uk, eliz AT is DOT elta DOT co DOT il
Cc: djgpp AT sun DOT soe DOT clarkson DOT edu
Subject: Re: .exe file format

> Date: Thu, 26 Oct 1995 13:46:32 +0200 (IST)
> From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
> 
> On Thu, 26 Oct 1995, A.Appleyard wrote:
> 
> > Where anywhere at all can I find information on the internal format and layout
> > of .COM and .EXE etc files?
> 
> Look in the Ralph Brown's Interrupt List (where else?), under the DOS 
> Exec function (4Bh).  There is a large table there which explains the 
> structure of all the executables.
> 
> > If a .COM file did start with `MZ' or `ZM', would that correspond with any
> > legal or likely PC instructions?
> 
> The first instruction of .COM file is at offset 100h.  DOS checks if the 
> first 2 bytes are "MZ" or "ZM", and if not, it assumes it's a .COM 
> program.  DOS ignores the file extension (but COMMAND.COM and other 
> shells don't, but that's another story).  So if a .COM starts with "MZ", 
> DOS will treat it as a .EXE program (actually, a few such ``hidden'' .EXE 
> programs come with DOS itself, so this behavior is intended).
> 
Furthermore, DOS EXEC system call can load and run any file, not only .COM
or .EXE
---
Alexander Lukyanov
lav AT video DOT yars DOT free DOT net