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In DOS memory administration, 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 time period for a number of incompatible know-how variants. The most generally used variant was the Expanded Memory Specification (EMS), which was developed jointly by Lotus Software, Intel, and Microsoft, in order that this specification was sometimes known as "LIM EMS". LIM EMS had three versions: 3.0, 3.2, and 4.0. The first widely carried out model was EMS 3.2, which supported up to 8 MiB of expanded memory and makes use of elements of the deal with house normally devoted to communication with peripherals (higher memory) to map parts of the expanded memory. EEMS, an expanded-memory management commonplace competing with LIM EMS 3.x, was developed by AST Research, Quadram and Ashton-Tate ("AQA"); it could map any space of the decrease 1 MiB. EEMS in the end was integrated in LIM EMS 4.0, which supported as much as 32 MiB of expanded memory and supplied some assist for DOS multitasking as nicely.

IBM, nonetheless, created its personal expanded-memory commonplace referred to as XMA. The usage of expanded memory became widespread with video games and enterprise applications reminiscent of Lotus 1-2-3 within the late 1980s by way of the mid-nineteen nineties, however its use declined as users switched from DOS to protected-mode operating methods resembling Linux, IBM OS/2, and Microsoft Windows. The 8088 processor of the IBM Laptop and IBM Computer/XT can deal with one megabyte (MiB, or 220 bytes) of memory. It inherited this limit from the 20-bit external deal with bus (and overall memory addressing structure) of the Intel 8086. The designers of the Computer allocated the decrease 640 KiB (655360 bytes) of handle area for read-write program memory (RAM), referred to as typical memory, and the remaining 384 KiB of memory house is reserved for makes use of such because the system BIOS, video memory, cognitive enhancement tool and memory on enlargement peripheral boards. Though the IBM Computer AT, introduced in 1984, uses the 80286 chip that can address as much as sixteen MiB of RAM as prolonged memory, it could only achieve this in protected mode.

The scarcity of software program compatible with protected mode (no commonplace DOS purposes can run in it) meant that the market was nonetheless open for one more solution. To make more memory accessible, a financial institution switching scheme was devised, where solely chosen elements of the additional memory is accessible at any given time. Initially, a single sixty four KiB (216 bytes) window of memory, referred to as a page frame, was used; later this was made more versatile. Applications are written in a particular solution to entry expanded memory. The window between typical memory and expanded memory can be adjusted to access completely different locations within the expanded memory. The primary publicly out there model of EMS, model 3.Zero allows entry of as much as four MiB of expanded memory. This was increased to eight MiB with model 3.2 of the specification. The ultimate version of EMS, model 4.Zero increased the maximum quantity of expanded memory to 32 MiB and supports extra functionality.

Microsoft thought that bank switching was an inelegant and momentary, however needed stopgap measure. Slamming his fist on the table throughout an interview Invoice Gates said of expanded memory, "It is rubbish! It's a kludge! … However we're going to do it". The companies deliberate to launch the standard on the Spring 1985 COMDEX, with many expansion-card and software program firms announcing their support. AST Analysis, STB Systems, Persyst, Quadram, and Tecmar rapidly 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 normal. The first public model of the EMS commonplace, known as EMS 3.0 was released in 1985; EMS 3.0, nevertheless, noticed virtually no hardware implementations earlier than being superseded by EMS 3.2. EMS 3.2 uses a 64 KiB region in the upper 384 KiB (higher memory area) divided into four 16 KiB pages, which can be used to map parts of the expanded memory. Quadram, cognitive enhancement tool AST, and Ashton-Tate created the Enhanced EMS (EEMS) commonplace.