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Expanded memory was a system of bank switching introduced around 1984 that provided more memory to byte-hungry, business-oriented MS-DOS programs. Bank switching (also known as "paging" but only loosely related to the ordinary meaning of " Paging " in computing was a technique common in 8-bit MS-DOS (short for M icro' s' oft D isk O perating S ystem is an Operating system commercialized by Microsoft. These were typically spreadsheets and databases running on the original IBM PC, and on its successors like the IBM XT and IBM AT. A spreadsheet is a Computer application that simulates a paper worksheet A Computer Database is a structured collection of records or data that is stored in a computer system The IBM Personal Computer XT, often shortened to the IBM XT or simply XT, was IBM's successor to the original IBM PC. The IBM Personal Computer/AT, more commonly known as the IBM AT and also sometimes called the PC AT or PC/AT, was IBM 's second-generation IBM PC and IBM XT had real mode memory architecture, which only allowed programs to use 1 megabyte (1 MiB) of address space, of which only up to 640 KB (640 KiB) was available for normal ram (the remainder from 640 KB to 1 megabyte being reserved for peripherals, most notably the screen memory in the display adapter and the bios code). Real mode, also called real address mode, is an operating mode of 80286 and later X86 -compatible CPUs. A mebibyte (a contraction of me ga bi nary byte) is a unit of Information or Computer storage, abbreviated MiB. A kibibyte (a contraction of ki lo bi nary byte) is a unit of Information or Computer storage, established by the International The IBM AT, which used an Intel 80286, supported protected mode, but it also ran MS-DOS, a real mode operating system that did not use extended memory directly. The Intel 286, introduced on February 1, 1982, (originally named 80286, and also called iAPX 286 in the programmer's manual In computing protected mode, also called protected virtual address mode, is an operational mode of X86 -compatible Central processing units (CPU An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination In computing Extended memory refers to memory above the first Megabyte of Address space in an IBM PC with an 80286 or later

The idea behind expanded memory was to use part of the remaining 384 KB, normally dedicated to communication with peripherals, for program memory as well. In order to fit potentially much more memory than the 384 KB of free address space would allow, a banking scheme was devised, where only selected portions of the additional memory would be accessible at the same time. Bank switching (also known as "paging" but only loosely related to the ordinary meaning of " Paging " in computing was a technique common in 8-bit Originally, a single 64 KB window of memory was possible; later this was made more flexible. Applications had to be written in a specific way in order to access expanded memory.

The Expanded Memory Specification (EMS) was developed jointly by Lotus, Intel, and Microsoft, so this specification was sometimes referred to as "LIM EMS". Lotus Software (called Lotus Development Corporation before its acquisition by IBM) is a Software company with headquarters in Westford, Microsoft Corporation is an American multinational Computer technology Corporation, which rose to dominate the Home computer

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Different implementations

Expansion boards

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. Industry Standard Architecture (in practice almost always shortened to ISA) was a Computer bus standard for IBM compatible computers 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. AST Research Inc was a Personal computer manufacturer founded in Irvine, California in 1980 by Albert Before proposing a merge request please see Talk and see if the merger you propose has recently been made and Given the price of RAM during the period, up to several hundred dollars per megabyte, and the quality and reputation of the above brand names, an expanded memory board was very expensive.

Motherboards

Later, some motherboards of Intel 80286-based computers implemented an expanded memory scheme that did not require add-on boards. A motherboard is the central or primary Printed circuit board (PCB making up a complex electronic system such as a modern Computer or Laptop The Intel 286, introduced on February 1, 1982, (originally named 80286, and also called iAPX 286 in the programmer's manual Typically, software switches determined how much memory should be used as expanded memory and how much should be used as extended memory. In computing Extended memory refers to memory above the first Megabyte of Address space in an IBM PC with an 80286 or later

Software emulation

Beginning in 1987, the built-in memory management features of Intel 80386 processor freely modeled the address space when running legacy real mode software, making hardware solutions unnecessary. Expanded memory could be simulated in software.

The first software expanded memory management (emulation) program was probably CEMM, available in November 1987 with Compaq DOS 3. CEMM, for Compaq Expanded Memory Manager was probably the first so-called PC " Memory manager " for Intel 80386 CPUs able to transform 31. A popular and well-featured commercial solution was Quarterdeck's QEMM. Quarterdeck Expanded Memory Manager (abbreviated QEMM sometimes pronounced ˈkwɛm though not by those who developed it is a Memory manager produced by Quarterdeck Office A contender was Qualitas' 386MAX. 386MAX (pronounced 386-to-the-max) was a computer Memory manager for DOS -based Personal computers It competed with Quarterdeck's Functionality was later incorporated into MS-DOS 4. 01 in 1989 and into DR-DOS 5. DR-DOS is a DOS -type Operating system for IBM PC - compatible Personal computers, originally developed by Gary Kildall 0 in 1990, as EMM386. Year 1990 ( MCMXC) was a Common year starting on Monday (link displays the 1990 Gregorian calendar) The name EMM386 was used for the Expanded memory managers of both Microsoft 's MS-DOS and Digital Research 's DR-DOS, which created

Software expanded memory managers in general offered additional, but closely related functionality. Notably, they could create ordinary memory areas (Upper Memory Blocks) in unused parts of the high 384 KB of real mode address space and provided tools for loading small programs, typically TSRs inside ("loadhi" or "loadhigh"). The Upper Memory Area (UMA is a design feature of IBM PC-compatible X86 Computers that was responsible for the 640 KB barrier. Terminate and Stay Resident (TSR is a System call in DOS operating systems that returns control to the system as if the program has quit but keeps the program in

Interaction between extended memory, expanded memory emulation and DOS extenders ended up being regulated by the XMS, VCPI and DPMI specifications. In computing Extended memory refers to memory above the first Megabyte of Address space in an IBM PC with an 80286 or later In computing the DOS Protected Mode Interface (DPMI is a specification introduced in 1989 which allows a DOS program to run in Protected mode, granting access to

Certain emulation programs, colloquially known as LIMulators, did not rely on motherboard or 80386 features at all. Instead, they reserved 64 KB of the base RAM for the expanded memory window, where they copied data to and from either extended memory or the hard disk when application programs requested page switches. This was programmatically easy to implement, but performance was low. This technique was offered by AboveDisk from Above Software and by several shareware programs. The term shareware, popularized by Bob Wallace, refers to Copyrighted commercial Software that is Distributed without payment on a trial

Details

An expanded memory board, being a hardware peripheral, needed a software device driver, which exported its services. In computing a device driver or software driver is a Computer program allowing higher-level computer programs to interact with a Hardware device Such a device driver was called "expanded memory manager". Its name was variable; the previously mentioned boards used remm. sys (AST), ps2emm. sys (IBM), aemm. sys (AT&T) and emm. sys (Intel) respectively. Later, the expression became associated with software-only solutions requiring the 80386 processor, for example Quarterdeck's QEMM (see below).

Expanded memory was a common term for several incompatible technology variants. The Expanded Memory Specification (EMS) was developed jointly by Lotus, Intel, and Microsoft, so this specification was sometimes referred to as "LIM EMS". Lotus Software (called Lotus Development Corporation before its acquisition by IBM) is a Software company with headquarters in Westford, Microsoft Corporation is an American multinational Computer technology Corporation, which rose to dominate the Home computer EEMS, a competing expanded memory management standard, was developed by AST Research, Quadram and Ashton-Tate. AST Research Inc was a Personal computer manufacturer founded in Irvine, California in 1980 by Albert Ashton-Tate ( Ashton-Tate Corporation) was a US based Software company best known for developing the popular DBASE Database application It allowed to also remap some or all of the lower 640 kB of memory, so that entire programs could be switched in and out of the extra RAM. The two standards were eventually combined as LIM EMS 4. 0.

See also

References

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL. The Free On-line Dictionary of Computing ( FOLDOC) is an online searchable encyclopedic Dictionary of Computing subjects The GNU Free Documentation License ( GNU FDL or simply GFDL) is a Copyleft License for free documentation designed by the Free Software

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