Loadhigh
Encyclopedia
Loadhigh is an internal MS-DOS
command
that is used to load a program into the upper memory area
(UMA) instead of conventional memory
. Due to design of the IBM PC
MS-DOS suffered from what was known as the 640 KiB 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 XMS
, EMS
and DOS extender
), 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 run-time. Therefore, it was often necessary to move some TSR
programs like the mouse driver or the SMARTDRV
disk caching driver prior to running a memory-hungry application. This was achieved by using loadhigh called with the program's name as the parameter.
The equivalent of loadhigh for device driver
s is DEVICEHIGH (usable only within CONFIG.SYS
).
Operating systems other than MS DOS run in protected mode
, support an unsegmented (flat) memory model and do not have a 640 kB constraint. Loadhigh and other methods of freeing conventional memory have become obsolete. This command is no longer available in the command interpreter of newer Windows
operating systems.
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
command
Command (computing)
In computing, a command is a directive to a computer program acting as an interpreter of some kind, in order to perform a specific task. Most commonly a command is a directive to some kind of command line interface, such as a shell....
that is used to load a program into the 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...
(UMA) instead of 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...
. Due to design of the IBM PC
IBM PC
The IBM Personal Computer, commonly known as the IBM PC, is the original version and progenitor of the IBM PC compatible hardware platform. It is IBM model number 5150, and was introduced on August 12, 1981...
MS-DOS suffered from what was known as the 640 KiB barrier. The size of this memory area, known as 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...
was fixed and independent of the amount of system memory actually installed. Various schemes were developed to support extra memory (see also XMS
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...
, EMS
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...
and DOS extender
DOS extender
A DOS extender is a computer software program which enables software to run under a protected mode environment even though the host operating system is only capable of operating in real mode....
), 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 run-time. Therefore, it was often necessary to move some TSR
Terminate and Stay Resident
Terminate and Stay Resident is a computer system call in DOS computer operating systems that returns control to the system as if the program has quit, but keeps the program in memory...
programs like the mouse driver or the SMARTDRV
SmartDrive
SmartDrive was a disk caching program that shipped with MS-DOS versions 4.01 through 6.22 and Windows 3.x. It improved disk transfer rates by storing frequently accessed data in the main memory. Early versions of SmartDrive were loaded through a CONFIG.SYS device driver named SMARTDRV.SYS...
disk caching driver prior to running a memory-hungry application. This was achieved by using loadhigh called with the program's name as the parameter.
The equivalent of loadhigh for 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....
s is DEVICEHIGH (usable only within 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 :...
).
Operating systems other than MS DOS run in protected mode
Protected mode
In computing, protected mode, also called protected virtual address mode, is an operational mode of x86-compatible central processing units...
, support an unsegmented (flat) memory model and do not have a 640 kB constraint. Loadhigh and other methods of freeing conventional memory have become obsolete. This command is no longer available in the command interpreter of newer 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...
operating systems.