HIMEM.SYS

HIMEM is an extended-memory manager --- a program that 
coordinates the use of your computer's extended memory, 
including the high memory area (HMA), so that no two 
applications or device drivers use the same memory at the same 
time.

You install HIMEM by adding a <DEVICE> command for HIMEM.SYS to 
your CONFIG.SYS file. The HIMEM.SYS command line must come 
before any commands that start applications or device drivers 
that use extended memory; for example, the HIMEM.SYS command 
line must come before the EMM386.EXE command line.

Note: When using HIMEM.SYS, you can also let MS-DOS 
automatically load itself to HMA (high memory area), so that a 
certain amount of conventional memory will be saved for other 
applications. To do this, add a line "DOS=HIGH" in your CONFIG.SYS 
file.

HIMEM.SYS for MS-DOS 5.0 ~ 6.22 checks for the integrity of the 
whole extended memory by default. HIMEM.SYS for MS-DOS 7.0 or 
7.1 doesn't do that by default. To specify whether to do memory 
checking, you can add a switch "TESTMEM:ON|OFF" to the command 
line loading HIMEM.SYS.

Windows 95 and 98 need HIMEM.SYS to be loaded before starting 
up.

To make HIMEM.SYS display memory information when it is loading, 
add a switch "VERBOSE" to your HIMEM.SYS command.

Extended memory: any memory over 1088 KB minus 16 byte is called 
extended memory in MS-DOS. It is because Byte FFFF:FFFF is the 
(65535 * 16 + 65536)th byte in memory.

For more information, please refer to MS-DOS Help or Windows NT 
command line command help.