Expanded Memory Specification (EMS)

Techopedia explains Expanded Memory Specification (EMS)

The latest version of expanded memory specification was developed in 1987 by Lotus Software, Intel and Microsoft.

The 8088 microprocessor only addressed a megabyte of memory. Thus, of the 1024 KB, 640 KB were used for RAM (Random Access Memory for reading and writing) and the remaining 384 Kb were used for system BIOS (basic input/output system), video memory and memory for peripheral expansion boards.

An expanded memory management standard, called extended EMS (EEMS) competed with LIM EMS. It was developed by AST Research, Quadram and Ashton-Tate which allowed entire programs to be switched in and out of the extra RAM. The two technologies were later combined into what became to be known as LIM EMS 4.0.

Later software switches were developed to determine how much memory could be used as expanded memory and how much could be used as extended memory, which is memory above 1024 KB. In around 1987, hardware solutions became no longer necessary as expanded memory could be created in software.

Still later software expanded memory managers were developed with additional but closely related functionality to EMS 4.0. They created RAM in unused parts of the 384 Kb called the upper memory area. This created space for loading small programs called TSRs (terminate and stay resident).

Until 1990, expanded memory was the preferred way to add memory to a PC. Then Windows 3.0 was released and used as an extended memory manager which enabled programs to use expanded memory without interfering with each other. Additionally, Windows 3.0 could simulate expanded memory for software applications requiring it.

EMS was used commonly in games and business programs from the late 1980s to the mid 1990s. Later, its use declined as consumers changed from the DOS operating system (OS) to Microsoft Windows OS.