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Besides the executable program itself, many EXE files contain other components called Resources , such as bitmaps and icons which the executable program may use for its Graphical User Interface .

The DOS Executable file format differs from the COM executable, which is limited to slightly less than 64 KiB in size and since it lacks relocation information, can only contain one Code Segment . The DOS executable header contains such relocation information, which allows multiple segments to be loaded at arbitrary memory addresses, and support executables larger than 64 KiB.

There are several main EXE File Formats .
  • DOS executable: These can only be identified by the ASCII string "MZ" or the hexadecimal 4D 5A at the beginning of the file (the " Magic Number "). These executables can be run from DOS, and most Windows versions can execute them using a sort of emulation. "MZ" are the initials of Mark Zbikowski , one of the developers of MS-DOS.

  • 16-bit New Executable : Introduced with Multitasking MS-DOS 4.0, these can be identified by the "NE" in ASCII. These cannot be run by any other version of DOS but can be run by all Windows and OS/2 versions .

  • Mixed 16/32-bit Linear Executable: Introduced with OS/2 2.0, these can be identified by the "LE" in ASCII. This format is not used for OS/2 applications anymore, but instead for VxD drivers under Windows 3.x and Windows 9x, and by some DOS extenders.

  • 32-bit Linear Executable: Introduced with OS/2 2.0, these can be identified by the "LX" in ASCII. These can only be run by OS/2 2.0 and higher . They are also used by some DOS Extender s.

  • '''32-bit , and also Windows 95 and higher, partially also in DOS using HX_DOS_Extender . They are also used in BeOS R3, however they somewhat violate the PE specification as they don't specify a correct subsystem .

  • 64-bit Portable Executable: Introduced by 64-bit versions of Windows, these are PE files with a CPU type corresponding to a 64-bit instruction set such as X86-64 or IA-64 . These can only be run by 64-bit editions of Microsoft Windows, such as Windows XP 64-Bit Edition or Windows Server 2003 64-Bit Edition , running on machines with the CPU type specified in the file.


Besides them, there are also many custom EXE formats, such as ''W3'' (a collection of LE files, only used in WIN386.EXE), ''W4'' (a compressed collection of LE files, only used in VMM32.VXD), ''DL'', ''MP'', ''P2'', ''P3'' (last three used by
Phar Lap extenders), and probably more .

When a 16-bit or 32-bit Windows executable is run by Windows, execution starts at either the NE or the PE, and ignores the MZ code. On the other hand, DOS cannot (except using HX DOS Extender for PE files only) execute these files. To prevent DOS from crashing, all Windows executable files must start with a working DOS program called "stub". . Normally this program simply displays a message that it cannot run in DOS mode, but there are a few dual-mode programs (MZ-NE or MZ-PE) (such as Regedit ) have a usable DOS section .

In Microsoft Windows , a user can expect that double-clicking on an exe file will open a program, unless it is incompatible or broken. This is useful in avoiding Computer Virus es. If a user receives a file that claims to be a picture or document, but it has the ".exe" extension, it is likely to be a virus or Trojan Horse that the sender is trying to trick them into running. This does not mean that all .exe files are viruses or trojans, just that many viruses and trojans are .exe files.


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