The MZ, at times, noted as ZM is a magic number for the file extension .exe supporting the binary and executable formats and can be extended to new, linear as well as the portable executable formats. The initials ZM or MZ refer to the name of Mark Zbikowski who put them into the original MS-DOS exec format. In as such, having the signature was necessary to create a distinguishing difference with other .EXE files from others that were considered much simpler like the .COM and the DOS formats.

The file can be easily identified by using the ASCII string MZ found at the beginning of the file. Compared to the COM format which is executable, the MZ Header is newer and different in that it contains information on relocation which allows users to access multiple segments that can be loaded on memory addresses as well as can support executable files slightly larger than the 64Kib. The only disadvantage of the MZ Header is that it requires little memory limits which apparently can be bypassed by the use of DOS extenders.

The executable found on the MZ Header can also run efficiently from DOS as well as 9x operating systems. Other 32 bit Windows can as well execute the MZ Header by using inbuilt virtual DOS machines. However, some of the graphical modes may not be supported by the MZ Header. On the other hand, 64-bit versions of Windows cannot execute the MZ Header. However, the DOSBox, Wine, and the DOSEMU are perfect alternative ways of running the MZ executable.

Moreover, it is considered that each and every PE file has a 16-bit DOS program. Due to that, when the file starts, it opens with the .EXE header. In the past, while people used the Microsoft Windows, The Windows 1.x, 2.x as well as 3.xx operating systems, they did not only exist in similar volumes as Microsoft DOS but equally ran with an MS-DOS operating system as well. As a matter of fact, it was highly likely that users found themselves attempting to run some of the programs in windows under the DOS.

Microsoft programmers, therefore, had to ensure that all windows programs had a 16-bit DOS program found at the front of each executable windows with the ability to alert users anytime they attempted to run any program under the Windows program operating under DOS. However, it cannot be considered to be more useful these days as it was back then when users and the world as a whole were transforming from the DOS to other systems and files that came after that. Notably, back then, it was not easy to find a program that could actually bind together a DOS version with a Win32 operating under the same single binary.

Additionally, users should know that the MZ Header is commonly used for backward compatibility. Moreover, it is considered the best to run on a program that has Win32 system as compared to others as well. Moreover, users should know that the MZ signature is commonly used by the MS-DOS relocatable 16-bit under the EXE format.