Expanded memory

In DOS memory management, expanded memory is a system of bank switching that provided additional memory to DOS programs beyond the limit of conventional memory (640 KB).

Expanded memory is an umbrella term for several incompatible technology variants. The most widely used variant was the Expanded Memory Specification (EMS), which was developed jointly by Lotus Software, Intel, and Microsoft, so that this specification was sometimes referred to as "LIM EMS." LIM EMS had several versions. The first widely implemented version was EMS 3.2, which supported up to 8 MB of expanded memory and uses parts of the address space normally dedicated to communication with peripherals (upper memory) to map portions of the expanded memory. EEMS, an expanded memory management standard competing with LIM EMS 3.x, was developed by AST Research, Quadram and Ashton-Tate; it could map any area of the lower 1 MB. EEMS ultimately was incorporated in LIM EMS 4.0, which supported up to 32 MB of expanded memory and provided some support for DOS multitasking as well. IBM however created its own expanded memory standard called XMA.