In computing,LOADHIGH (abbreviatedLH) is an internalDOScommand inCOMMAND.COM that is used to load a program into theupper memory area (UMA) instead ofconventional memory.^[1]

The command was introduced withMS-DOS 5.0 /PC DOS 5.0 in 1991,^[2][1] copying the built-inHILOAD command earlier introduced withDR 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 theIBM PC, DOS suffered from what was known as the640 KB barrier. The size of this memory area, known asconventional memory, was fixed and independent of the amount of system memory actually installed. Various schemes were developed to support extra memory (see alsoEMS,XMS) andDOS 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 someTSR programs like themouse driver or the disk caching driver (likeSMARTDRV) prior to running a memory-hungry application. This was achieved by usingLOADHIGH called with the program's name as the parameter.

To load TSRs high withinCONFIG.SYS, theINSTALLHIGH directive must be used instead of theLOADHIGH command. The equivalent ofLOADHIGH fordevice drivers isDEVICEHIGH (usable only withinCONFIG.SYS).These are also supported since DR DOS 6.0. DR DOS 5.0 and higher also supportHIINSTALL andHIDEVICE, respectively.^[4]

Most modern operating systems now run inprotected 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 theWindows XPMS-DOS subsystem to maintain MS-DOS and MS OS/2 version 1.x syntax compatibility only.^[5] It is not available at all onWindows XP 64-Bit Edition^[6] and also no longer available in thecommand interpreter of newerWindows operating systems.^{[7][clarification needed]}

• 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
• Self-relocation

• Cooper, Jim (2001).Special Edition Using MS-DOS 6.22 (3 ed.).Que Publishing.ISBN 978-0-7897-2573-8.
• Ivens, Kathy; Proffit, Brian (1993).OS/2 Inside & Out.Osborne McGraw-Hill.ISBN 978-0-07-881871-4.

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