page_title: Expanded memory
section_title: Expansion boards
hierarchical_section_title: Expanded memory / Implementations / Expansion boards
caption_attribution_description: Emulex Persyst 4Mib ISA memory board, 460 g, 9x12 chips
context_page_description: 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.
  Expanded memory is an umbrella term for several incompatible technology variants. The most widely used variant was the Expanded Memory Specification, 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 MiB of expanded memory and uses parts of the address space normally dedicated to communication with peripherals 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 MiB. EEMS ultimately was incorporated in LIM EMS 4.0, which supported up to 32 MiB of expanded memory and provided some support for DOS multitasking as well. IBM, however, created its own expanded-memory standard called XMA.
context_section_description: This insertion of a memory window into the peripheral address space could originally be accomplished only through specific expansion boards, plugged into the ISA expansion bus of the computer. Famous 1980s expanded memory boards were AST RAMpage, IBM PS/2 80286 Memory Expansion Option, AT&T Expanded Memory Adapter and the Intel Above Board. Given the price of RAM during the period, up to several hundred dollars per MiB, and the quality and reputation of the above brand names, an expanded memory board was very expensive.
caption: Emulex Persyst 4 MiB ISA memory board
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