EMS – Expanded Memory Specification

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.

There are several versions of EMS. The original versions, called EMS 3.0 and 3.2, enable programs to use an additional 8MB of memory, but for data only. An improved version developed by AST, Quadram and Ashton-Tate is known as EEMS (Extended EMS). EEMS enables programs to use extra memory for code as well as for data. The most recent version of EMS (created in 1987) is known as EMS 4.0 or LIM 4.0, LIM being the initials of the three companies that developed the specification: Lotus, Intel, and Microsoft. EMS 4.0 raises the available amount of memory to 32MB.

Until the release of Microsoft Windows 3.0 in 1990, expanded memory was the preferred way to add memory to a PC. The alternative method, called extended memory, was less flexible and could be used only by special programs such as RAM disks. Windows 3.0 and all later versions of Windows, however, contain an extended memory managerthat enables programs to use extended memory without interfering with one another. In addition, Windows can simulate expanded memory for those programs that need it (by using the EMM386.EXE driver).

Webopedia Staff
Since 1995, more than 100 tech experts and researchers have kept Webopedia’s definitions, articles, and study guides up to date. For more information on current editorial staff, please visit our About page.

Top Articles

The Complete List of 1500+ Common Text Abbreviations & Acronyms

Text Abbreviations reviewed by Web Webster   From A3 to ZZZ we list 1,559 SMS, online chat, and text abbreviations to help you translate and understand...

Windows Operating System History & Versions

The Windows operating system (Windows OS) refers to a family of operating systems developed by Microsoft Corporation. We look at the history of Windows...

How to Create a Website Shortcut on Your Desktop

Website Shortcut on Your Desktop reviewed by Web Webster   This Webopedia guide will show you how to create a website shortcut on your desktop using...

Generations of Computers (1st to 5th)

Reviewed by Web Webster Learn about each of the 5 generations of computers and major technology developments that have led to the computing devices that...

Pareto Principle

The Pareto Principle holds that 80 percent of consequences can come from 20...

Thumb Drive

A thumb drive, or USB flash drive, is a small device with flash...

Pipeline

A pipeline is a figurative measurement of client or customer progress through a...