expanded memory


Memory used through EMS. In systems based on Intel 80386 or later processor expanded memory is part of the extended memory that is mapped into the expanded memory page frame by the processor. The mapping is controlled by the EMM. In earlier systems, a dedicated EMS hardware adapter is needed to map memory into the page frame. In both cases, an appropriate device driver is needed for the proper communication between hardware and EMM.

Last updated: 1996-01-10

expanded memory manager

<software, storage>

(EMM) IBM PC memory manager software implementing Expanded Memory Specification, such as EMM386 or QEMM386. EMMs can usually provide UMB as well.

Last updated: 1996-01-10

expanded memory page frame


The part of the IBM PC reserved memory address space used by EMS.

Last updated: 1996-01-10

Expanded Memory Specification


(EMS) An IBM PC memory paging scheme enabling access to memory other than conventional memory in real mode.

Expanded memory is provided through a page frame of at least 64 kilobytes in the reserved memory address region. Access to this memory is provided by an expanded memory manager (EMM) software. The EMM functions are accessible through interrupt 67H.

In 8086 or 8088 based systems this is the only way to use memory beyond conventional memory. In systems based on 80286 or later, XMS and HMA provide alternative methods.

EMS was developed jointly by Lotus, Intel, and Microsoft prior to 1988. Accordingly, this specification is sometimes referred to as LIM EMS.

A complete discussion of EMS and programming examples can be found in ["PC System Programming for developers", 1989, ISBN 1-55755-035-2 (Book only) and ISBN 1-55755-036-0 (Book and diskette)].

EEMS, a competing expanded memory management standard, was developed by AST Research, Quadram and Ashton-Tate.

See also upper memory block.

Last updated: 1996-01-10

Nearby terms:

EXOSexpanded memoryexpanded memory managerexpanded memory page frame

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