The MZ EXE File Format

The MZ EXE File Format


Original Documentation

The old EXE files are the EXE files executed directly by MS-DOS. They were a
major improvement over the old 64K COM files, since EXE files can span multiple
segments. An EXE file consists of three different parts, the header, the
relocation table and the binary code.
The header is expanded by a lot of programs to store their copyright information
in the executable, some extensions are documented below.
The format of the header is as follows :
OFFSET              Count TYPE   Description
0000h                   2 char   ID='MZ'
								 ID='ZM'
0002h                   1 word   Number of bytes in last 512-byte page
								 of executable
0004h                   1 word   Total number of 512-byte pages in executable
								 (including the last page)
0006h                   1 word   Number of relocation entries
0008h                   1 word   Header size in paragraphs
000Ah                   1 word   Minimum paragraphs of memory allocated in
								 addition to the code size
000Ch                   1 word   Maximum number of paragraphs allocated in
								 addition to the code size
000Eh                   1 word   Initial SS relative to start of executable
0010h                   1 word   Initial SP
0012h                   1 word   Checksum (or 0) of executable
0014h                   1 dword  CS:IP relative to start of executable
								 (entry point)
0018h                   1 word   Offset of relocation table;
								 40h for new-(NE,LE,LX,W3,PE etc.) executable
001Ah                   1 word   Overlay number (0h = main program)

Following are the header expansions by some other prorams like TLink, LZExe and
other linkers, encryptors and compressors; all offsets are relative to the start
of the whole header :

---new executable
OFFSET              Count TYPE   Description
001Ch                   4 byte   ????
0020h                   1 word   Behaviour bits ??
0022h                  26 byte   reserved (0)
003Ch                   1 dword  Offset of new executable header from start of
								 file (or 0 if plain MZ executable)

---Borland TLINK
OFFSET              Count TYPE   Description
001Ch                   2 byte   ?? (apparently always 01h 00h)
001Eh                   1 byte   ID=0FBh
001Fh                   1 byte   TLink version, major in high nybble
0020h                   2 byte   ??

---old ARJ self-extracting archive
OFFSET              Count TYPE   Description
001Ch                   4 char   ID='RJSX' (older versions)
								 new signature is 'aRJsf'" in the first 1000
								 bytes of the file)
---LZEXE compressed executable
OFFSET              Count TYPE   Description
001Ch                   2 char   ID='LZ'
001Eh                   2 char   Version number :
								  '09' - LZExe 0.90
								  '91' - LZExe 0.91
---PKLITE compressed executable
OFFSET              Count TYPE   Description
001Ch                   1 byte   Minor version number
001Dh                   1 byte   Bit mapped :
								 0-3 - major version
								   4 - Extra compression
								   5 - Multi-segment file
001Eh                   6 char   ID='PKLITE'
---LHarc 1.x self-extracting archive
OFFSET              Count TYPE   Description
001Ch                   4 byte   unused???
0020h                   3 byte   Jump to start of extraction code
0023h                   2 byte   ???
0025h                  12 char   ID='LHarc's SFX '
--LHA 2.x self-extracting archive
OFFSET              Count TYPE   Description
001Ch                   8 byte   ???
0024h                  10 char   ID='LHa's SFX '
								 For version 2.10
								 ID='LHA's SFX ' (v2.13)
								 For version 2.13
---LH self-extracting archive
OFFSET              Count TYPE   Description
001Ch                   8 byte   ???
0024h                   8 byte   ID='LH's SFX '
---TopSpeed C 3.0 CRUNCH compressed file
OFFSET              Count TYPE   Description
001Ch                   1 dword  ID=018A0001h
0020h                   1 word   ID=1565h
---PKARC 3.5 self-extracting archive
OFFSET              Count TYPE   Description
001Ch                   1 dword  ID=00020001h
0020h                   1 word   ID=0700h
---BSA (Soviet archiver) self-extracting archive
OFFSET              Count TYPE   Description
001Ch                   1 word   ID=000Fh
001Eh                   1 byte   ID=A7h
---LARC self-extracting archive
OFFSET              Count TYPE   Description
001Ch                   4 byte   ???
0020h                  11 byte   ID='SFX by LARC '

After the header, there follow the relocation items, which are used to span
multpile segments. The relocation items have the following format :
OFFSET              Count TYPE   Description
0000h                   1 word   Offset within segment
0002h                   1 word   Segment of relocation
To get the position of the relocation within the file, you have to compute the
physical adress from the segment:offset pair, which is done by multiplying the
segment by 16 and adding the offset and then adding the offset of the binary
start. Note that the raw binary code starts on a paragraph boundary within the
executable file. All segments are relative to the start of the executable in
memory, and this value must be added to every segment if relocation is done
manually.

EXTENSION:EXE,OVR,OVL
OCCURENCES:PC
PROGRAMS:MS-DOS
REFERENCE:Ralf Brown's Interrupt List
SEE ALSO:COM,EXE,NE EXE

This information is from Corion.net and is used with permission.

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