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study/sabre/os/files/Executables/COM.txt

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+COM Format
+Intel byte order
+
+Information from File Format List 2.0 by Max Maischein.
+
+--------!-CONTACT_INFO----------------------
+If you notice any mistakes or omissions, please let me know!  It is only
+with YOUR help that the list can continue to grow.  Please send
+all changes to me rather than distributing a modified version of the list.
+
+This file has been authored in the style of the INTERxxy.* file list
+by Ralf Brown, and uses almost the same format.
+
+Please read the file FILEFMTS.1ST before asking me any questions. You may find
+that they have already been addressed.
+
+         Max Maischein
+
+Max Maischein, 2:244/1106.17
+Max_Maischein@spam.fido.de
+corion@informatik.uni-frankfurt.de
+Corion on #coders@IRC
+--------!-DISCLAIMER------------------------
+DISCLAIMER:  THIS MATERIAL IS PROVIDED "AS IS".  I verify the information
+contained in this list to the best of my ability, but I cannot be held
+responsible for any problems caused by use or misuse of the information,
+especially for those file formats foreign to the PC, like AMIGA or SUN file
+formats. If an information it is marked "guesswork" or undocumented, you
+should check it carefully to make sure your program will not break with
+an unexpected value (and please let me know whether or not it works
+the same way).
+
+Information marked with "???" is known to be incomplete or guesswork.
+
+Some file formats were not released by their creators, others are regarded
+as proprietary, which means that if your programs deal with them, you might
+be looking for trouble. I don't care about this.
+--------------------------------------------
+
+The COM files are raw binary executables and are a leftover from the old CP/M
+machines with 64K RAM.  A COM program can only have a size of less than one
+segment (64K), including code and static data since no fixups for segment
+relocation or anything else is included. One method to check for a COM file is
+to check if the first byte in the file could be a valid jump or call opcode, but
+this is a very weak test since a COM file is not required to start with a jump
+or a call. In principle, a COM file is just loaded at offset 100h in the segment
+and then executed.
+
+OFFSET              Count TYPE   Description
+0000h                   1 byte   ID=0E9h
+                                 ID=0EBh
+                                 Those are not safe ways to determine wether a
+                                 file is a COM file or not, but most COM files
+                                 start with a jump.
+Further information not available.
+EXTENSION:COM
+OCCURENCES:PC
+SEE ALSO:EXE,MZ EXE,NE EXE