EXE

Overview
The EXE format has its root in MS-DOS and is still widely used today. The first versions were pore DOS executables, identified by either "MZ" or "ZM" as the first two bytes. Later on, lots of additional formats were added, like Windows' NE (New Executable) extension, OS/2's LE and LX (Linear Executable), and later Win32's PE executable (a variant of COFF), as well as some DOS extenders adding overlays, resources and other information into it.

Resources

 * Ralf Brown's Interrupt List, INT 21h, Function 4Bh, describes lots of the "older" style EXE formats
 * Microsoft has a document on the PE specification
 * article on the PE format as used by Windows NT 3 by Johannes Plachy