DOS MZ executable
| Filename extension | .exe |
|---|---|
| Magic number | MZ |
| Type of format | Binary, executable |
| Extended to | New Executable Linear Executable Portable Executable |
The DOS MZ executable format is the executable file format used for .EXE files in DOS.
The file can be identified by the ASCII string "MZ" or the hexadecimal 4D 5A at the beginning of the file (the "magic number"). "MZ" are the initials of Mark Zbikowski, one of the developers of MS-DOS. This is used partly because it disassembles as "dec bp; pop dx" (intel syntax), which no COM file will contain as it is an unpredictable result (could crash) and just doesn't do anything useful. Because command.com (the command interpreter on MS-DOS) exceded the 64 KiB limit, Microsoft made MS-DOS decide whether to load a given executable as a .com or an MZ based on this magic number rather than the filename.
The MZ DOS executable file is newer than the COM executable format and differs from it. The DOS executable header contains relocation information, which allows multiple segments to be loaded at arbitrary memory addresses, and it supports executables larger than 64 KiB; however, the format still requires relatively low memory limits. These limits were later bypassed using DOS extenders.
The environment of an EXE program run by DOS is found in its Program Segment Prefix.
Compatibility
MZ DOS executables can be run from DOS and Windows 9x-based operating systems. 32-bit Windows NT-based operating systems can execute them using their built-in Virtual DOS machine (although some graphics modes are unsupported). 64-bit versions of Windows cannot execute them. Alternative ways to run these executables include DOSBox, DOSEMU and Wine.
MZ DOS executables can be created by linkers, like Digital Mars Optlink, MS linker, VALX or Open Watcom's WLINK; additionally, FASM can create them directly.
See also
External links
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