HIMEM.SYS is a DOS

DOS

DOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...

 device driver

Device driver

In computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device....

 which allows DOS programs to store data in extended memory

Extended memory

In DOS memory management, extended memory refers to memory above the first megabyte of address space in an IBM PC or compatible with an 80286 or later processor. The term is mainly used under the DOS and Windows operating systems...

 via the Extended Memory Specification (XMS). This device driver is of particular importance because various versions of Microsoft Windows

Microsoft Windows

Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

 that ran on top of the DOS operating system required HIMEM.SYS to be loaded to be able to run.

As of MS-DOS 5.0, HIMEM.SYS was introduced and could be used to load the DOS kernel code into the High Memory Area (HMA) to increase the amount of available conventional memory

Conventional memory

In DOS memory management, conventional memory, also called base memory, is the first 640 kilobytes of the memory on IBM PC or compatible systems. It is the read-write memory usable by the operating system and application programs...

 by specifying DOS=HIGH in CONFIG.SYS

CONFIG.SYS

CONFIG.SYS is the primary configuration file for the DOS, OS/2 as well as similar operating systems. It is a special file that contains setup or configuration instructions for the computer system.- Usage :...

.

HIMEM.SYS provides access to the memory beyond the first 1 MB of space and thus is required by Windows 9x

Windows 9x

Windows 9x is a generic term referring to a series of Microsoft Windows computer operating systems produced since 1995, which were based on the original and later modified Windows 95 kernel...

/Me

Windows Me

Windows Millennium Edition, or Windows Me , is a graphical operating system released on September 14, 2000 by Microsoft, and was the last operating system released in the Windows 9x series. Support for Windows Me ended on July 11, 2006....

 in order to load the graphical portions of the operating systems.
In FreeDOS

FreeDOS

FreeDOS is an operating system for IBM PC compatible computers. FreeDOS is made up of many different, separate programs that act as "packages" to the overall FreeDOS Project...

, the matching file is named HIMEM.EXE and can be loaded from the FreeDOS configuration file named FDCONFIG.SYS or CONFIG.SYS.

In Windows 9x

Windows 9x

Windows 9x is a generic term referring to a series of Microsoft Windows computer operating systems produced since 1995, which were based on the original and later modified Windows 95 kernel...

, there is also a command-line loadable version of HIMEM.SYS called XMSMMGR.EXE. It can load extended memory services after the system has booted into the command prompt. This allowed Windows Setup to load even if HIMEM.SYS was not loaded.

See also

• Conventional memory
  Conventional memory
  In DOS memory management, conventional memory, also called base memory, is the first 640 kilobytes of the memory on IBM PC or compatible systems. It is the read-write memory usable by the operating system and application programs...
  
  
• Extended memory
  Extended memory
  In DOS memory management, extended memory refers to memory above the first megabyte of address space in an IBM PC or compatible with an 80286 or later processor. The term is mainly used under the DOS and Windows operating systems...
  
  
• Expanded memory
  Expanded memory
  In DOS memory management, expanded memory is a system of bank switching introduced April 24, 1985 that provided additional memory to DOS programs beyond the limit of conventional memory. Expanded memory uses parts of the address space normally dedicated to communication with peripherals for program...
  
  
• High memory area
• Upper memory area
  Upper Memory Area
  In DOS memory management, the upper memory area refers to memory between the addresses of 640 KB and 1024 KB in an IBM PC or compatible. IBM reserved the uppermost 384 KB of the 8088 CPU's 1024 KB address space for ROM, RAM on peripherals, and memory-mapped input/output...
  
  
• EMM386
  EMM386
  The name EMM386 was used for the expanded memory managers of both Microsoft's MS-DOS and Digital Research's DR-DOS, which created expanded memory using extended memory on Intel 80386 CPUs. There also is an EMM386.EXE available in FreeDOS....
  
  
• Memory manager
  Memory manager
  In IBM PC compatible computing, DOS memory management refers to software and techniques employed to give applications access to more than 640K of "conventional memory". The 640kB limit was specific to the IBM PC and close compatibles; other machines running MS-DOS had different limits, for example...