This specification
defines one method of extending the amount of
memory that a processor can address from the conventional
memory area. It uses an area outside of
system memory to store information. An Expanded
Memory Manager (EMM) provides a window view
into this larger data area. The old 3.2 EMS specification
requires a 64 KB window in the Upper Memory
Block (UMB). The newer 4.0 specification can create
this window anywhere in conventional or UMB
memory.
eXtended Memory Specification (XMS)
A device driver that emulates expanded memory by
using extended memory (the memory above the 1 MB
limit imposed by DOS). The original version of this
specification (developed by Quarterdeck) appeared
in 1986. It allowed an 80286 or above processor to
access up to 64 KB of extended memory from within
the conventional memory area by enabling the A20
address line. This specification makes it possible to
multitask from within DOS by freeing more application
memory. In 1990, Microsoft revised its
HIMEM.SYS
driver with the release of Windows 3.0.
The scope of XMS memory increased to multitask
Windows applications. Versions of Windows
starting with Windows NT don??™t require
HIMEM.
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