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Extended Memory
Extended memory is internal system RAM above 1024 KB.
MS-DOS or your applications (that support extended
memory) can access Extended memory if your system is
configured with an extended memory driver (
XMS).
Extended memory drivers manage the extended memory
ensuring that two programs do not use the same part of
memory. The enhanced mode of MS Windows uses
extended memory to multitask applications.
MS-DOS includes the HIMEM.SYS extended memory driver.
HIMEM.SYS is defined in your CONFIG.SYS file where it is
automatically loaded each time you boot the system.
HIMEM.SYS also enables MS-DOS programs to use an extra
64-KB region located just above the 1-MB mark for storage
of code and data. This area is known as high memory area
(
HMA).
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Note: MS-DOS can also be loaded in HMA to free up
conventional memory. Refer to your MS-DOS User’s Manual
for instructions.
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Note: Some application programs that run in 386
enhanced mode (such as Windows) require special extended
memory managers. Use the extended memory manager
provided with your application, if available. Otherwise, use
HIMEM.SYS, the MS-DOS version furnished with your
computer.
You can define part of extended memory as one or more
RAM disks using the RAMDRIVE.SYS device driver. Details are
provided in the next section.
Memory Areas
Configuring Memory F-3