The DOS MZ executable format is the
executable
In computing, executable code, an executable file, or an executable program, sometimes simply referred to as an executable or binary, causes a computer "to perform indicated tasks according to encoded instruction (computer science), instructi ...
file format
A file format is a standard way that information is encoded for storage in a computer file. It specifies how bits are used to encode information in a digital storage medium. File formats may be either proprietary or free.
Some file formats ...
used for .
EXE
Exe or EXE may refer to:
* .exe, a file extension
* exe., abbreviation for executive
Places
* River Exe, in England
* Exe Estuary, in England
* Exe Island, in Exeter, England
Transportation and vehicles
* Exe (locomotive), a British locomotive
...
files in
DOS
DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems.
DOS may also refer to:
Computing
* Data over signalling (DoS), multiplexing data onto a signalling channel
* Denial-of-service attack (DoS), an attack on a communicat ...
.
The file can be identified by the
ASCII
ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of ...
string "MZ" (
hexadecimal
In mathematics and computing, the hexadecimal (also base-16 or simply hex) numeral system is a positional numeral system that represents numbers using a radix (base) of 16. Unlike the decimal system representing numbers using 10 symbols, hexa ...
: 4D 5A) at the beginning of the file (the "
magic number"). "MZ" are the initials of
Mark Zbikowski
Mark "Zibo" Joseph Zbikowski (born March 21, 1956) is a former Microsoft Architect and an early computer hacker. He started working at the company only a few years after its inception, leading efforts in MS-DOS, OS/2, Cairo and Windows NT. In 2006 ...
, one of the leading developers of
MS-DOS
MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few ope ...
.
Inside Windows: An In-Depth Look into the Win32 Portable Executable File Format - MSDN Magazine, February 2002
. "Every PE file begins with a small MS-DOS executable. ... The first bytes of a PE file begin with the traditional MS-DOS header, called an IMAGE_DOS_HEADER. The only two values of any importance are e_magic and e_lfanew. ... The e_magic field (a WORD) needs to be set to the value 0x5A4D. ... In ASCII representation, 0x5A4D is MZ, the initials of Mark Zbikowski, one of the original architects of MS-DOS."
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 64k; however, the format still requires relatively low memory limits. These limits were later bypassed using DOS extender
A DOS extender is a computer software program running under DOS that enables software to run in a protected mode environment even though the host operating system is only capable of operating in real mode.
DOS extenders were initially developed ...
s.
Segment handling
The environment of an EXE program run by DOS is found in its Program Segment Prefix
The Program Segment Prefix (PSP) is a data structure used in DOS systems to store the state of a program. It resembles the Zero Page in the CP/M operating system. The PSP has the following structure:
The PSP is most often used to get the comm ...
.
EXE files normally have separate segments for the code, data, and stack. Program execution begins at address 0 of the code segment
In computing, a code segment, also known as a text segment or simply as text, is a portion of an object file or the corresponding section of the program's virtual address space that contains executable instructions.
Segment
The term "segment" ...
, and the stack pointer register is set to whatever value is contained in the header information (thus if the header specifies a 512 byte stack, the stack pointer is set to 200h). It is possible to not use a separate stack segment and simply use the code segment for the stack if desired.
The DS (data segment
In computing, a data segment (often denoted .data) is a portion of an object file or the corresponding address space of a program that contains initialized static variables, that is, global variables and static local variables. The size of this seg ...
) register normally contains the same value as the CS (code segment) register and is not loaded with the actual segment address of the data segment when an EXE file is initialized; it is necessary for the programmer to set it themselves, generally done via the following instructions:
MOV AX, @DATA
MOV DS, AX
Termination
In the original DOS 1.x API
The DOS API is an API which originated with 86-DOS and is used in MS-DOS/ PC DOS and other DOS-compatible operating systems. Most calls to the DOS API are invoked using software interrupt 21h ( INT 21h). By calling INT 21h with a subfunction ...
, it was also necessary to have the CS register pointing to the segment with the PSP at program termination; this was done via the following instructions:
PUSH DS
XOR AX, AX
PUSH AX
Program termination would then be performed by a RETF instruction, which would retrieve the original segment address with the PSP from the stack and then jump to address 0, which contained an INT 20h instruction.
The DOS 2.x API
The DOS API is an API which originated with 86-DOS and is used in MS-DOS/ PC DOS and other DOS-compatible operating systems. Most calls to the DOS API are invoked using software interrupt 21h ( INT 21h). By calling INT 21h with a subfunction ...
introduced a new program termination function, INT 21h Function 4Ch which does not require saving the PSP segment address at the start of the program, and Microsoft advised against the use of the older DOS 1.x method.
Compatibility
MZ DOS executables can be run from DOS and Windows 9x
Windows 9x is a generic term referring to a series of Microsoft Windows computer operating systems produced from 1995 to 2000, which were based on the Windows 95 kernel and its underlying foundation of MS-DOS, both of which were updated in subs ...
-based operating systems. 32-bit Windows NT
Windows NT is a proprietary graphical operating system
An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.
Time-sharing operating systems sc ...
-based operating systems can execute them using their built-in Virtual DOS machine
Virtual DOS machines (VDM) refer to a technology that allows running 16-bit/32-bit DOS and 16-bit Windows programs when there is already another operating system running and controlling the hardware.
Overview
Virtual DOS machines can operate ei ...
(although some graphics modes are unsupported). 64-bit versions of Windows cannot execute them. Alternative ways to run these executables include DOSBox
DOSBox is a free and open-source emulator which runs software for MS-DOS compatible disk operating systems—primarily video games. It was first released in 2002, when DOS technology was becoming obsolete. Its adoption for running DOS games i ...
and DOSEMU.
MZ DOS executables can be created by linkers, like Digital Mars
Digital Mars is a small American software company owned by Walter Bright and based in Vienna, Virginia, that makes C, C++ and D compilers, and associated utilities such as an integrated development environment (IDE) for Windows and DOS, which D ...
Optlink
This article describes the calling conventions used when programming x86 architecture microprocessors.
Calling conventions describe the interface of called code:
*The order in which atomic (scalar) parameters, or individual parts of a complex pa ...
, MS linker
MS, ms, Ms, M.S., etc. may refer to:
Arts and entertainment
* ''Ms.'' (magazine), an American feminist magazine
* Metal Storm (webzine), a heavy metal website based in Estonia
Businesses and organizations
* MS-13, criminal gang
* Missionaries ...
, VALX or Open Watcom
Watcom C/C++ (currently Open Watcom C/C++) is an integrated development environment (IDE) product from Watcom International Corporation for the C, C++, and Fortran programming languages. Watcom C/C++ was a commercial product until it was discon ...
's WLINK; additionally, FASM
FASM (''flat assembler'') is an assembler for x86 processors. It supports Intel-style assembly language on the IA-32 and x86-64 computer architectures. It claims high speed, size optimizations, operating system (OS) portability, and macro abil ...
can create them directly.
See also
* DOS
DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems.
DOS may also refer to:
Computing
* Data over signalling (DoS), multiplexing data onto a signalling channel
* Denial-of-service attack (DoS), an attack on a communicat ...
* DOS extender
A DOS extender is a computer software program running under DOS that enables software to run in a protected mode environment even though the host operating system is only capable of operating in real mode.
DOS extenders were initially developed ...
* Portable Executable
The Portable Executable (PE) format is a file format for executables, object code, DLLs and others used in 32-bit and 64-bit versions of Windows operating systems. The PE format is a data structure that encapsulates the information necessary fo ...
* DOS API
The DOS API is an API which originated with 86-DOS and is used in MS-DOS/ PC DOS and other DOS-compatible operating systems. Most calls to the DOS API are invoked using software interrupt 21h ( INT 21h). By calling INT 21h with a subfunctio ...
* Executable compression
Executable compression is any means of compressing an executable file and combining the compressed data with decompression code into a single executable. When this compressed executable is executed, the decompression code recreates the origina ...
Further reading
*
References
External links
A closer look at EXE DOS stub
{{Disk operating systems
Executable file formats
DOS technology