Using RAM

Manufacturers of personal computers have adopted the following names to describe the functions of various parts of RAM:

Conventional memory

Upper memory

High memory

Extended memory

Expanded memory

The following memory map shows how RAM is allocated.

Memory Map

This diagram illustrates how your computer allocates memory. Although memory size is referred to in thousands of bytes (characters), or in kilobytes, the actual quantities are slightly larger. This is because a kilobyte is actually 1,024 bytes (210), not 1,000 bytes. Memory measurements are usually rounded off to simplify discussion.

Conventional Memory

MS-DOS can directly access only 1 megabyte (1024 kilobytes) of memory at a time. This is the area between 0KB and 1MB on the memory map. The first 640 kilobytes in this area is called conventional memory.

Conventional memory is used as a work area by MS-DOS and most application software.

Extended BIOS Data Area

This is 1KB of RAM loaded at 639KB. It is used to support extended BIOS functions including support for PS/2 pointing devices.

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Toshiba T2150CD user manual Using RAM, Memory Map, Conventional Memory, Extended Bios Data Area