The MS-DOS COM Executable File Format

Original Documentation

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

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