In DOS memory management, expanded memory is a system of financial institution switching that provided additional memory to DOS programs beyond the limit of conventional memory (640 KiB). Expanded memory is an umbrella term for a number of incompatible technology variants. The most widely used variant was the Expanded Memory Specification (EMS), which was developed jointly by Lotus Software program, Intel, and Microsoft, so that this specification was generally referred to as "LIM EMS". LIM EMS had three versions: 3.0, 3.2, and 4.0. The first broadly carried out version was EMS 3.2, which supported up to 8 MiB of expanded memory and uses elements of the deal with space usually devoted to communication with peripherals (upper memory) to map portions of the expanded memory. EEMS, an expanded-Memory Wave management commonplace competing with LIM EMS 3.x, was developed by AST Analysis, Quadram and Ashton-Tate ("AQA"); it could map any space of the decrease 1 MiB. EEMS ultimately was incorporated in LIM EMS 4.0, which supported as much as 32 MiB of expanded memory and supplied some support for DOS multitasking as nicely.

IBM, nonetheless, created its own expanded-memory normal known as XMA. The use of expanded memory turned widespread with video games and enterprise applications resembling Lotus 1-2-3 in the late 1980s by means of the mid-nineteen nineties, but its use declined as users switched from DOS to protected-mode operating programs corresponding to Linux, IBM OS/2, and Microsoft Home windows. The 8088 processor of the IBM Pc and IBM Laptop/XT can handle one megabyte (MiB, or 220 bytes) of memory. It inherited this limit from the 20-bit exterior handle bus (and total memory addressing structure) of the Intel 8086. The designers of the Pc allotted the lower 640 KiB (655360 bytes) of deal with space for Memory Wave read-write program memory (RAM), called standard memory, and the remaining 384 KiB of memory area is reserved for uses such as the system BIOS, video memory, and memory on enlargement peripheral boards. Regardless that the IBM Computer AT, launched in 1984, uses the 80286 chip that may handle as much as sixteen MiB of RAM as extended memory, it can solely do so in protected mode.

The scarcity of software program appropriate with protected mode (no standard DOS applications can run in it) meant that the market was nonetheless open for an additional answer. To make extra memory accessible, a bank switching scheme was devised, where only selected components of the extra memory is accessible at any given time. Initially, a single sixty four KiB (216 bytes) window of memory, called a web page frame, was used; later this was made extra flexible. Applications are written in a specific approach to entry expanded memory. The window between typical memory and expanded memory could be adjusted to access completely different areas inside the expanded Memory Wave Experience. The first publicly out there model of EMS, version 3.Zero permits access of as much as four MiB of expanded memory. This was increased to eight MiB with model 3.2 of the specification. The final version of EMS, version 4.Zero increased the utmost quantity of expanded memory to 32 MiB and supports additional functionality.

Microsoft thought that financial institution switching was an inelegant and momentary, however necessary stopgap measure. Slamming his fist on the table during an interview Invoice Gates said of expanded memory, "It is rubbish! It's a kludge! … But we will do it". The companies deliberate to launch the usual at the Spring 1985 COMDEX, with many expansion-card and software program companies saying their support. AST Research, STB Methods, Persyst, Quadram, and Memory Wave Experience Tecmar shortly designed EMS-compliant cards to compete with Intel's personal Above Board growth card. By mid-1985 some already referred to as EMS a de facto customary. The primary public model of the EMS normal, referred to as EMS 3.0 was released in 1985; EMS 3.0, nonetheless, saw nearly no hardware implementations before being superseded by EMS 3.2. EMS 3.2 makes use of a sixty four KiB region within the upper 384 KiB (upper memory space) divided into four 16 KiB pages, which can be used to map portions of the expanded memory. Quadram, AST, and Ashton-Tate created the Enhanced EMS (EEMS) commonplace.