Developer(s) | Digital Research, Novell, Microsoft, IBM, Caldera |
---|---|
Initial release | 11 June 1991 |
Operating system | DOS |
Type | Command |
In computing, LOADHIGH
(abbreviated LH
) 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.
[1]
The command was introduced with
MS-DOS 5.0 /
PC DOS 5.0 in 1991,
[2]
[1] copying the built-in HILOAD
command earlier introduced with
DR DOS 5.0 in 1990.
DR DOS 6.0 added support for this naming variant as well in 1991.
[3]
[4]
Due to design of the
IBM PC, 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) 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 driver or the disk caching driver (like
SMARTDRV) prior to running a memory-hungry application. This was achieved by using LOADHIGH
called with the program's name as the parameter.
To load TSRs high within
CONFIG.SYS, the
INSTALLHIGH directive must be used instead of the LOADHIGH
command. The equivalent of LOADHIGH
for
device drivers is
DEVICEHIGH (usable only within
CONFIG.SYS).
These are also supported since DR DOS 6.0. DR DOS 5.0 and higher also support
HIINSTALL and
HIDEVICE, respectively.
[4]
Most modern operating systems now run in
protected mode with support for an unsegmented (flat) memory model and do not have a 640 KB constraint. LOADHIGH
and other methods of freeing conventional memory have largely become obsolete.
LOADHIGH
is part of the
Windows XP
MS-DOS subsystem to maintain MS-DOS and MS OS/2 version 1.x syntax compatibility only.
[5] It is not available at all on
Windows XP 64-Bit Edition
[6] and also no longer available in the
command interpreter of newer
Windows operating systems.
[7][
clarification needed]
Windows XP does not use this command. It is accepted only for compatibility with MS-DOS files.
Developer(s) | Digital Research, Novell, Microsoft, IBM, Caldera |
---|---|
Initial release | 11 June 1991 |
Operating system | DOS |
Type | Command |
In computing, LOADHIGH
(abbreviated LH
) 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.
[1]
The command was introduced with
MS-DOS 5.0 /
PC DOS 5.0 in 1991,
[2]
[1] copying the built-in HILOAD
command earlier introduced with
DR DOS 5.0 in 1990.
DR DOS 6.0 added support for this naming variant as well in 1991.
[3]
[4]
Due to design of the
IBM PC, 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) 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 driver or the disk caching driver (like
SMARTDRV) prior to running a memory-hungry application. This was achieved by using LOADHIGH
called with the program's name as the parameter.
To load TSRs high within
CONFIG.SYS, the
INSTALLHIGH directive must be used instead of the LOADHIGH
command. The equivalent of LOADHIGH
for
device drivers is
DEVICEHIGH (usable only within
CONFIG.SYS).
These are also supported since DR DOS 6.0. DR DOS 5.0 and higher also support
HIINSTALL and
HIDEVICE, respectively.
[4]
Most modern operating systems now run in
protected mode with support for an unsegmented (flat) memory model and do not have a 640 KB constraint. LOADHIGH
and other methods of freeing conventional memory have largely become obsolete.
LOADHIGH
is part of the
Windows XP
MS-DOS subsystem to maintain MS-DOS and MS OS/2 version 1.x syntax compatibility only.
[5] It is not available at all on
Windows XP 64-Bit Edition
[6] and also no longer available in the
command interpreter of newer
Windows operating systems.
[7][
clarification needed]
Windows XP does not use this command. It is accepted only for compatibility with MS-DOS files.