In computing, (abbreviated ) is an internal
DOS command in
COMMAND.COM that is used to load a program into the
upper memory area (UMA) instead of
conventional memory.
The command was introduced with
MS-DOS 5.0
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 ...
/
PC DOS 5.0 in 1991,
copying the built-in command earlier introduced with
DR DOS 5.0 in 1990.
DR DOS 6.0 added support for this naming variant as well in 1991.
Overview
Due to design of the
IBM PC
The IBM Personal Computer (model 5150, commonly known as the IBM PC) is the first microcomputer released in the IBM PC model line and the basis for the IBM PC compatible de facto standard. Released on August 12, 1981, it was created by a team ...
, DOS suffered from what was known as the
640 KB barrier. The size of this memory area, known as
conventional memory, was fixed and independent of the amount of system memory actually installed. Various schemes were developed to support extra memory (see also
EMS,
XMS
XMS may refer to:
* Cray XMS, a vector processor minisupercomputer
* eBuddy XMS, instant-messaging service
* ISO 639:xms, Moroccan Sign Language
* Macas Airport (IATA: XMS), Ecuador
* XMS Capital Partners, a global financial services firm
* eXten ...
) and
DOS extenders, but conventional memory was still an issue due to compatibility issues. It was a scarce resource as many applications demanded a large part of this basic memory fragment at runtime. Therefore, it was often necessary to move high some
TSR programs like the
mouse
A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...
driver or the disk caching driver (like
SMARTDRV
SmartDrive (or SMARTDRV) is a disk caching program shipped with MS-DOS versions 4.01 through 6.22 and Windows 3.0 through Windows 3.11. It improves data transfer rates by storing frequently accessed data in random-access memory (RAM).
Early v ...
) prior to running a memory-hungry application. This was achieved by using called with the program's name as the parameter.
To load TSRs high within
CONFIG.SYS
CONFIG.SYS is the primary configuration file for the DOS and OS/2 operating systems. It is a special ASCII text file that contains user-accessible setup or configuration directives evaluated by the operating system's DOS BIOS (typically residing ...
, the
INSTALLHIGH directive must be used instead of the command. The equivalent of for
device driver
In computing, a device driver is a computer program that operates or controls a particular type of device that is attached to a computer or automaton. A driver provides a software interface to hardware devices, enabling operating systems and ot ...
s is
DEVICEHIGH (usable only within
CONFIG.SYS
CONFIG.SYS is the primary configuration file for the DOS and OS/2 operating systems. It is a special ASCII text file that contains user-accessible setup or configuration directives evaluated by the operating system's DOS BIOS (typically residing ...
).
These are also supported since DR DOS 6.0. DR DOS 5.0 and higher also support
HIINSTALL and
HIDEVICE, respectively.
Most modern operating systems now run in
protected mode
In computing, protected mode, also called protected virtual address mode, is an operational mode of x86-compatible central processing units (CPUs). It allows system software to use features such as virtual memory, paging and safe multi-tasking d ...
with support for an unsegmented (flat) memory model and do not have a 640 KB constraint. and other methods of freeing conventional memory have largely become obsolete.
is part of the
Windows XP MS-DOS subsystem to maintain MS-DOS and MS OS/2 version 1.x syntax compatibility only.
It is not available at all on
Windows XP 64-Bit Edition and also no longer available in the
command interpreter of newer
Windows operating systems.
See also
*
BUFFERSHIGH /
HIBUFFERS (DOS 7.0+)
*
STACKSHIGH /
HISTACKS (DOS 7.0+)
*
LASTDRIVEHIGH /
HILASTDRIVE (DOS 7.0+)
*
FILESHIGH /
HIFILES (DOS 7.0+)
*
FCBSHIGH /
HIFCBS (DOS 7.0+)
*
DOS /
HIDOS (DOS 5.0+)
*
DOSDATA
*
HIINSTALLLAST
*
List of DOS commands
*
Self-highloading
In computer programming, a self-relocating program is a program that relocates its own address-dependent instructions and data when run, and is therefore capable of being loaded into memory at any address. In many cases, self-relocating code is a ...
*
Self-relocation
In computer programming, a self-relocating program is a program that relocates its own address-dependent instructions and data when run, and is therefore capable of being loaded into memory at any address. In many cases, self-relocating code is ...
References
Further reading
*
*
Internal DOS commands
DOS memory management
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