Write down short notes about Extended and Expanded memory.

Subject Microprocessor and Assembly Language
NU Year Set: 5.(b) Marks: 3 Year: 2011

Extended memory, also known as XMS (eXtended Memory Specification) is a technology that enables capacity above the 640KB standard MS-DOS limit of main memory.

Extended memory was introduced in the Intel 80286 processor, increasing the amount of addressable memory beyond what was introduced in the similarly named expanded memory (EMS). Prior to XMS, expanded memory was used to increase the 640KB upper limit of DOS to 1MB using a gated memory card riser.

Extended memory initially boosted the addressable memory to 16MB. XMS 2.0 extended the capacity to 64GB and XMS 3.0 to up to 4GB. Beyond XMS 3.0, AMD64, the de facto x86-64standard, expands maximum memory to 256TB


Expanded Memory Specification (EMS), or expanded memory, is a technique for utilizing more than 1MB of main memory in DOS -based computers. The limit of 1MB is built into the DOS operating system. The upper 384K is reserved for special purposes, leaving just 640K of conventional memory for programs.

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