EMS (Expanded Memory Specification)

Expanded memory works by using some of the DOS reserved memory address space to access memory on the Intel memory board. The area of reserved address space used to access expanded memory is made up of 16Kb sections called pages. A minimum of four contiguous 16Kb pages are taken from the reserved DOS memory between 640K and 1 Mb. Typically, the address space used is between 768K and 896K. This 64Kb area is used as a mappable space and is known as the Expanded Memory Page Frame. Additional unused 16Kb pages found in the reserved memory area can also be assigned to expanded memory. Having expanded memory requires that you have an Expanded Memory Manager (EMM.SYS for Intel memory boards), to "manage" the expanded memory. The driver associates (or maps) the pages of physical memory on the memory board to the pages in the reserved DOS area. Only programs written to use expanded memory can utilize expanded memory. Some examples of applications that use expanded memory are Lotus 123 version 2.x and WordPerfect 5.x.

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Last Update: 6:27 PM 11/28/01