![Expanded memory](https://upload.wikimedia.org/wikipedia/commons/f/fe/Expanded_memory.svg)
In
DOS memory management
In IBM PC compatible computing, DOS memory management refers to software and techniques employed to give applications access to more than 640 kibibytes (640*1024 bytes) (KiB) of "conventional memory". The 640 KiB limit was specific to the IBM PC ...
, expanded memory is a system of
bank switching
Bank switching is a technique used in computer design to increase the amount of usable memory beyond the amount directly addressable by the processor instructions. It can be used to configure a system differently at different times; for example ...
that provided additional memory to
DOS
DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems.
DOS may also refer to:
Computing
* Data over signalling (DoS), multiplexing data onto a signalling channel
* Denial-of-service attack (DoS), an attack on a communicatio ...
programs beyond the limit of
conventional memory
In DOS memory management, conventional memory, also called base memory, is the first 640 kilobytes of the memory on IBM PC or compatible systems. It is the read-write memory directly addressable by the processor for use by the operating system ...
(640 KiB).
''Expanded memory'' is an umbrella term for several incompatible technology variants. The most widely used variant was the Expanded Memory Specification (EMS), which was developed jointly by
Lotus Software
Lotus Software (called Lotus Development Corporation before its acquisition by IBM) was an American software company based in Massachusetts; it was "offloaded" to India's HCL Technologies in 2018.
Lotus is most commonly known for the Lotus 1-2- ...
,
Intel
Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the developers of the x86 seri ...
, and
Microsoft
Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washing ...
, so that this specification was sometimes referred to as "LIM EMS". LIM EMS had several versions. The first widely implemented version was EMS 3.2, which supported up to 8 MiB of expanded memory and uses parts of the address space normally dedicated to communication with peripherals (
upper memory
In DOS memory management, the upper memory area (UMA) refers to memory between the addresses of 640 KB and 1024 KB ( 0xA0000–0xFFFFF) in an IBM PC or compatible. IBM reserved the uppermost 384 KB of the 8088 CPU's 1024 KB ...
) to map portions of the expanded memory. EEMS, an expanded-memory management standard competing with LIM EMS 3.x, was developed by
AST Research
AST Research, Inc., later doing business as AST Computer, was a personal computer manufacturer. It was founded in 1980 in Irvine, California by Albert Wong, Safi Qureshey, and Thomas Yuen, as an initialism of their first names. In the 1980s, AS ...
,
Quadram
Intelligent Systems Corporation (ISC) was an American technology company that sold portable computers, video terminals, expansion cards, and other peripherals through a variety of manufacturing subsidiaries. Founded in 1973, the company restruct ...
and
Ashton-Tate ("AQA"); it could map any area of the lower 1 MiB. EEMS ultimately was incorporated in LIM EMS 4.0, which supported up to 32 MiB of expanded memory and provided some support for DOS multitasking as well. IBM, however, created its own expanded-memory standard called XMA.
The use of expanded memory became common with games and business programs such as
Lotus 1-2-3
Lotus 1-2-3 is a discontinued spreadsheet program from Lotus Software (later part of IBM). It was the first killer application of the IBM PC, was hugely popular in the 1980s, and significantly contributed to the success of IBM PC-compatibles i ...
in the late 1980s through the mid-1990s, but its use declined as users switched from DOS to
protected-mode
In computing, protected mode, also called protected virtual address mode, is an operational mode of x86-compatible central processing units (CPUs). It allows system software to use features such as virtual memory, paging and safe multi-tasking d ...
operating systems such as
Linux
Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...
,
IBM OS/2, and
Microsoft Windows
Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...
.
Background
![Expanded memory description 1](https://upload.wikimedia.org/wikipedia/commons/a/a2/Expanded_memory_description_1.svg)
The
8088
The Intel 8088 ("''eighty-eighty-eight''", also called iAPX 88) microprocessor is a variant of the Intel 8086. Introduced on June 1, 1979, the 8088 has an eight-bit external data bus instead of the 16-bit bus of the 8086. The 16-bit registers and ...
processor of the
IBM PC
The IBM Personal Computer (model 5150, commonly known as the IBM PC) is the first microcomputer released in the IBM PC model line and the basis for the IBM PC compatible de facto standard. Released on August 12, 1981, it was created by a team ...
and
IBM PC/XT
The IBM Personal Computer XT (model 5160, often shortened to PC/XT) is the second computer in the IBM Personal Computer line, released on March 8, 1983. Except for the addition of a built-in hard drive and extra expansion slots, it is very simila ...
could address one
megabyte
The megabyte is a multiple of the unit byte for digital information. Its recommended unit symbol is MB. The unit prefix ''mega'' is a multiplier of (106) in the International System of Units (SI). Therefore, one megabyte is one million bytes o ...
(MiB, or 2
20 bytes) of memory. It inherited this limit from the 20-bit external address bus of the
Intel 8086
The 8086 (also called iAPX 86) is a 16-bit microprocessor chip designed by Intel between early 1976 and June 8, 1978, when it was released. The Intel 8088, released July 1, 1979, is a slightly modified chip with an external 8-bit data bus (allowi ...
. The designers of the PC allocated the lower 640
KiB
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable unit ...
( bytes) of address space for read-write program memory (RAM), called "conventional memory", and the remaining 384 KiB of memory space was reserved for uses such as the system
BIOS
In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the ...
, video memory, and memory on expansion peripheral boards.
Even though the
IBM PC AT
The IBM Personal Computer/AT (model 5170, abbreviated as IBM AT or PC/AT) was released in 1984 as the fourth model in the IBM Personal Computer line, following the IBM PC/XT and its IBM Portable PC variant. It was designed around the Intel 8028 ...
, introduced in 1984, used the
80286
The Intel 80286 (also marketed as the iAPX 286 and often called Intel 286) is a 16-bit microprocessor that was introduced on February 1, 1982. It was the first 8086-based CPU with separate, non-multiplexed address and data buses and also the fi ...
chip that could address up to 16 MiB of RAM as
extended memory
In DOS memory management, extended memory refers to memory above the first megabyte (220 bytes) of address space in an IBM PC or compatible with an 80286 or later processor. The term is mainly used under the DOS and Windows operating systems. DOS ...
, it could only do so in
protected mode
In computing, protected mode, also called protected virtual address mode, is an operational mode of x86-compatible central processing units (CPUs). It allows system software to use features such as virtual memory, paging and safe multi-tasking d ...
. The scarcity of software compatible with the 286 protected mode (no standard
DOS
DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems.
DOS may also refer to:
Computing
* Data over signalling (DoS), multiplexing data onto a signalling channel
* Denial-of-service attack (DoS), an attack on a communicatio ...
applications could run in it) meant that the market was still open for another solution.
To fit potentially much more memory than the 384 KiB of free address space would allow, a
bank switching
Bank switching is a technique used in computer design to increase the amount of usable memory beyond the amount directly addressable by the processor instructions. It can be used to configure a system differently at different times; for example ...
scheme was devised, where only selected parts of the additional memory would be accessible at any given time. Originally, a single 64 KiB (2
16 bytes) window of memory, called a
page frame
A page, memory page, or virtual page is a fixed-length contiguous block of virtual memory, described by a single entry in the page table. It is the smallest unit of data for memory management in a virtual memory operating system. Similarly, a p ...
, was possible; later this was made more flexible. Programs had to be written in a specific way to access expanded memory. The "window" between lower RAM and expanded RAM could be moved to different locations within the Expanded RAM.
A first attempt to use a bank switching technique was made by Tall Tree Systems with their JRAM boards,
but these did not catch on.
(Tall Tree Systems later made EMS-based boards using the same JRAM brand.)
Expanded Memory Specification (EMS)
Lotus Development
Lotus Software (called Lotus Development Corporation before its acquisition by IBM) was an American software company based in Massachusetts; it was "offloaded" to India's HCL Technologies in 2018.
Lotus is most commonly known for the Lotus 1-2- ...
,
Intel
Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the developers of the x86 seri ...
, and
Microsoft
Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washing ...
cooperated to develop the EMS standard (aka LIM EMS). The first publicly available version of EMS, version 3.0 allowed access of up to 4 MiB of expanded memory. This was increased to 8 MiB with version 3.2 of the specification. The final version of EMS, version 4.0 increased the maximum amount of expanded memory to 32 MiB and supported additional functionality.
Microsoft thought that bank switching was an inelegant and temporary, but necessary stopgap measure. Slamming his fist on the table during an interview
Bill Gates
William Henry Gates III (born October 28, 1955) is an American business magnate and philanthropist. He is a co-founder of Microsoft, along with his late childhood friend Paul Allen. During his career at Microsoft, Gates held the positions ...
said of expanded memory, "It's garbage! It's a
kludge
A kludge or kluge () is a workaround or quick-and-dirty solution that is clumsy, inelegant, inefficient, difficult to extend and hard to maintain. This term is used in diverse fields such as computer science, aerospace engineering, Internet sla ...
! … But we're going to do it". The companies planned to launch the standard at the Spring 1985
COMDEX
COMDEX (an abbreviation of COMputer Dealers' EXhibition) was a computer expo trade show held in the Las Vegas Valley of Nevada, United States, each November from 1979 to 2003. It was one of the largest computer trade shows in the world, usually ...
, with many expansion-card and software companies announcing their support.
The first public version of the EMS standard, called EMS 3.0 was released in 1985; EMS 3.0, however, saw almost no hardware implementations before being superseded by EMS 3.2.
EMS 3.2 used a 64 KiB region in the upper 384 KiB (
upper memory
In DOS memory management, the upper memory area (UMA) refers to memory between the addresses of 640 KB and 1024 KB ( 0xA0000–0xFFFFF) in an IBM PC or compatible. IBM reserved the uppermost 384 KB of the 8088 CPU's 1024 KB ...
area) divided into four 16 KiB pages, which could be used to map portions of the expanded memory.
In turn, EMS 3.2 was improved upon by a group of three other companies: AST Research, Quadram and Ashton-Tate, which created their own Enhanced EMS (EEMS) standard. EEMS allowed any 16 KiB region in lower RAM to be mapped to expanded memory, as long as it was not associated with interrupts or dedicated I/O memory such as network or video cards. Thus, entire programs could be switched in and out of the extra RAM. EEMS also added support for two sets of mapping registers. These features were used by early DOS multitasker software such as
DESQview
DESQview (DV) is a text mode multitasking operating environment developed by Quarterdeck Office Systems which enjoyed modest popularity in the late 1980s and early 1990s. Running on top of DOS, it allows users to run multiple programs concurrentl ...
. Released in 1987, the LIM EMS 4.0 specification incorporated practically all features of EEMS.
A new feature added in LIM EMS 4.0 was that EMS boards could have multiple sets of page-mapping registers (up to 64 sets). This allowed a primitive form of DOS
multitasking. The caveat was, however, that the standard did not specify how many register sets a board should have, so there was great variability between hardware implementations in this respect.
The Expanded Memory Specification (EMS) is the specification describing the use of expanded memory. EMS functions are accessible through software
interrupt
In digital computers, an interrupt (sometimes referred to as a trap) is a request for the processor to ''interrupt'' currently executing code (when permitted), so that the event can be processed in a timely manner. If the request is accepted, ...
67h. Programs using EMS must first establish the presence of an installed expanded memory manager (EMM) by checking for a device driver with the device name EMMXXXX0.
Expanded Memory Adapter (XMA)
IBM developed their own memory standard called Expanded Memory Adapter (XMA); the IBM DOS driver for it was XMAEM.SYS. Unlike EMS, the IBM expansion boards could be addressed both using an expanded memory model and as
extended memory
In DOS memory management, extended memory refers to memory above the first megabyte (220 bytes) of address space in an IBM PC or compatible with an 80286 or later processor. The term is mainly used under the DOS and Windows operating systems. DOS ...
.
The expanded memory hardware interface used by XMA boards is, however, incompatible with EMS,
but a XMA2EMS.SYS driver provided EMS emulation for XMA boards.
XMA boards were first introduced for the 1986 (revamped) models of the
3270 PC.
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. Famous 1980s expanded memory boards were
AST RAMpage, IBM PS/2 80286 Memory Expansion Option,
AT&T
AT&T Inc. is an American multinational telecommunications holding company headquartered at Whitacre Tower in Downtown Dallas, Texas. It is the world's largest telecommunications company by revenue and the third largest provider of mobile tel ...
Expanded Memory Adapter and the
Intel
Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the developers of the x86 seri ...
Above Board. Given the price of RAM during the period, up to several hundred dollars per MiB, and the quality and reputation of the above brand names, an expanded memory board was very expensive.
Motherboard chipsets
Later, some
motherboard
A motherboard (also called mainboard, main circuit board, mb, mboard, backplane board, base board, system board, logic board (only in Apple computers) or mobo) is the main printed circuit board (PCB) in general-purpose computers and other expand ...
chipset
In a computer system, a chipset is a set of electronic components
An electronic component is any basic discrete device or physical entity in an electronic system used to affect electrons or their associated fields. Electronic components are ...
s of
Intel 80286
The Intel 80286 (also marketed as the iAPX 286 and often called Intel 286) is a 16-bit microprocessor that was introduced on February 1, 1982. It was the first 8086-based CPU with separate, non-multiplexed address and data buses and also the fi ...
-based computers implemented an expanded memory scheme that did not require add-on boards, notably the
NEAT chipset
The NEAT chipset (the acronym standing for "New Enhanced AT") is a
4 chip VLSI implementation (including the 82C206 IPC) of the control logic used in the IBM PC compatible PC/AT computers. It consists of the 82C211 CPU/Bus controller, 82C212 Pag ...
. Typically, software switches determined how much memory should be used as ''expanded memory'' and how much should be used as ''
extended memory
In DOS memory management, extended memory refers to memory above the first megabyte (220 bytes) of address space in an IBM PC or compatible with an 80286 or later processor. The term is mainly used under the DOS and Windows operating systems. DOS ...
''.
Device drivers
An expanded-memory board, being a hardware peripheral, needed a software
device driver
In computing, a device driver is a computer program that operates or controls a particular type of device that is attached to a computer or automaton. A driver provides a software interface to hardware devices, enabling operating systems and ot ...
, which exported its services. 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
Intel 80386
The Intel 386, originally released as 80386 and later renamed i386, is a 32-bit microprocessor introduced in 1985. The first versions had 275,000 transistors[Quarterdeck
The quarterdeck is a raised deck behind the main mast of a sailing ship. Traditionally it was where the captain commanded his vessel and where the ship's colours were kept. This led to its use as the main ceremonial and reception area on bo ...]
's
QEMM
Quarterdeck Expanded Memory Manager (QEMM) is a memory manager produced by Quarterdeck Office Systems in the late 1980s through the late 1990s. It was the most popular third-party memory manager for the MS-DOS and other DOS operating systems.
...
,
Qualitas'
386MAX or the default
EMM386
EMM386 is the expanded memory manager of Microsoft's MS-DOS, IBM's PC DOS, Digital Research's DR-DOS, and Datalight's ROM-DOS which is used to create expanded memory using extended memory on Intel 80386 CPUs. There also is an EMM386.EXE available ...
in MS-DOS, PC DOS and DR-DOS.
Software emulation
Beginning in 1986, the built-in memory management features of
Intel 80386
The Intel 386, originally released as 80386 and later renamed i386, is a 32-bit microprocessor introduced in 1985. The first versions had 275,000 transistors[CEMM
CEMM, for Compaq Expanded Memory Manager was the first so-called PC " memory manager" for Intel 80386 CPUs, able to provide expanded memory (EMS) emulation by using the virtual memory features and the virtual 8086 mode of the CPU.
It was present i ...]
, available in September 1986 as a utility for the
Compaq Deskpro 386
The Deskpro 386 was a line of desktop computers in Compaq's Deskpro range of IBM PC compatibles. The computers featured Intel's 32-bit 80386 microprocessor. Introduced in September 1986, the Deskpro 386 was the first implementation of the 80386 pro ...
. A popular and well-featured commercial solution was Quarterdeck's QEMM. A contender was Qualitas'
386MAX. Functionality was later incorporated into
MS-DOS 4.01 in 1989 and into
DR DOS 5.0 in 1990, as
EMM386
EMM386 is the expanded memory manager of Microsoft's MS-DOS, IBM's PC DOS, Digital Research's DR-DOS, and Datalight's ROM-DOS which is used to create expanded memory using extended memory on Intel 80386 CPUs. There also is an EMM386.EXE available ...
.
Software expanded-memory managers in general offered additional, but closely related functionality. Notably, they allowed using parts of the
upper memory area
In DOS memory management, the upper memory area (UMA) refers to memory between the addresses of 640 KB and 1024 KB ( 0xA0000–0xFFFFF) in an IBM PC or compatible. IBM reserved the uppermost 384 KB of the 8088 CPU's 1024 KB ...
(UMA) (the upper 384 KiB of real-mode address space) called ''upper memory blocks'' (UMBs) and provided tools for loading small programs, typically
TSRs inside ("LOADHI" or "LOADHIGH").
Interaction between
extended memory
In DOS memory management, extended memory refers to memory above the first megabyte (220 bytes) of address space in an IBM PC or compatible with an 80286 or later processor. The term is mainly used under the DOS and Windows operating systems. DOS ...
, expanded-memory emulation and DOS extenders ended up being regulated by the XMS,
Virtual Control Program Interface
In computing, the Virtual Control Program Interface (VCPI) is a specification published in 1989 by Phar Lap Software that allows a DOS program to run in protected mode, granting access to many features of the processor not available in real mode ...
(VCPI),
DOS Protected Mode Interface
In computing, the DOS Protected Mode Interface (DPMI) is a specification introduced in 1989 which allows a DOS program to run in protected mode, giving access to many features of the new PC processors of the time not available in real mode. It w ...
(DPMI) and
DOS Protected Mode Services
DOS Protected Mode Services (DPMS) is a set of extended DOS memory management services to allow DPMS-enabled DOS drivers to load and execute in extended memory and protected mode.
Not being a DOS extender by itself, DPMS is a minimal set of ex ...
(DPMS) specifications.
Certain emulation programs, colloquially known as LIMulators, did not rely on motherboard or 80386 features at all. Instead, they reserved 64 KiB 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
Shareware is a type of proprietary software that is initially shared by the owner for trial use at little or no cost. Often the software has limited functionality or incomplete documentation until the user sends payment to the software developer ...
programs.
It is also possible to emulate EMS by using XMS memory on 286 CPUs using 3rd party utilities like EMM286 (.SYS driver).
Decline
Expanded Memory usage declined in the 1990s. The IBM AT
Intel 80286
The Intel 80286 (also marketed as the iAPX 286 and often called Intel 286) is a 16-bit microprocessor that was introduced on February 1, 1982. It was the first 8086-based CPU with separate, non-multiplexed address and data buses and also the fi ...
supported 24 bits of address space (16 MiB) in
protected mode
In computing, protected mode, also called protected virtual address mode, is an operational mode of x86-compatible central processing units (CPUs). It allows system software to use features such as virtual memory, paging and safe multi-tasking d ...
, and the 386 supported 32-bit addresses, or 4
gigabyte
The gigabyte () is a multiple of the unit byte for digital information. The prefix ''giga'' means 109 in the International System of Units (SI). Therefore, one gigabyte is one billion bytes. The unit symbol for the gigabyte is GB.
This defini ...
s (2
32) of RAM – 4096 times the addressable space of the original 8086. DOS itself did not directly support protected mode, but Microsoft eventually developed
DPMI, and several
DOS extender
A DOS extender is a computer software program running under DOS that enables software to run in a protected mode environment even though the host operating system is only capable of operating in real mode.
DOS extenders were initially developed ...
s were published based on it. DOS programs like ''
Doom
Doom is another name for damnation.
Doom may also refer to:
People
* Doom (professional wrestling), the tag team of Ron Simmons and Butch Reed
* Daniel Doom (born 1934), Belgian cyclist
* Debbie Doom (born 1963), American softball pitcher
* L ...
'' could use extenders like
DOS/4G
DOS/4G is a 32-bit DOS extender developed by Rational Systems (later Tenberry Software). It allows DOS programs to eliminate the 640 KB conventional memory limit by addressing up to 64 MB of extended memory on Intel 80386 and above machines.
...
to run in protected mode while still using the
DOS API
The DOS API is an API which originated with 86-DOS and is used in MS-DOS/ PC DOS and other DOS-compatible operating systems. Most calls to the DOS API are invoked using software interrupt 21h ( INT 21h). By calling INT 21h with a subfunction ...
. In the early 1990s new operating systems like
Linux
Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...
,
Windows 9x
Windows 9x is a generic term referring to a series of Microsoft Windows computer operating systems produced from 1995 to 2000, which were based on the Windows 95 kernel and its underlying foundation of MS-DOS, both of which were updated in subs ...
,
Windows NT
Windows NT is a proprietary graphical operating system
An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.
Time-sharing operating systems sc ...
,
OS/2
OS/2 (Operating System/2) is a series of computer operating systems, initially created by Microsoft and IBM under the leadership of IBM software designer Ed Iacobucci. As a result of a feud between the two companies over how to position OS/2 ...
, and
BSD/OS
BSD/OS (originally called BSD/386 and sometimes known as BSDi) is a discontinued proprietary version of the BSD operating system developed by Berkeley Software Design, Inc. (BSDi).
BSD/OS had a reputation for reliability in server roles; the reno ...
supported protected mode "out of the box". These and similar developments rendered Expanded Memory an obsolete concept.
See also
*
Conventional memory
In DOS memory management, conventional memory, also called base memory, is the first 640 kilobytes of the memory on IBM PC or compatible systems. It is the read-write memory directly addressable by the processor for use by the operating system ...
*
DOS memory management
In IBM PC compatible computing, DOS memory management refers to software and techniques employed to give applications access to more than 640 kibibytes (640*1024 bytes) (KiB) of "conventional memory". The 640 KiB limit was specific to the IBM PC ...
*
Extended memory
In DOS memory management, extended memory refers to memory above the first megabyte (220 bytes) of address space in an IBM PC or compatible with an 80286 or later processor. The term is mainly used under the DOS and Windows operating systems. DOS ...
(XMS)
*
High memory area
In DOS memory management, the high memory area (HMA) is the RAM area consisting of the first 65520 bytes above the one megabyte in an IBM AT or compatible computer.
In real mode, the segmentation architecture of the Intel 8086 and subsequen ...
(HMA)
*
Overlay (programming)
In a general computing sense, overlaying means "the process of transferring a block of program code or other data into main memory, replacing what is already stored". Overlaying is a programming method that allows programs to be larger than th ...
*
Upper memory area
In DOS memory management, the upper memory area (UMA) refers to memory between the addresses of 640 KB and 1024 KB ( 0xA0000–0xFFFFF) in an IBM PC or compatible. IBM reserved the uppermost 384 KB of the 8088 CPU's 1024 KB ...
(UMA)
*
Global EMM Import Specification
EMM386 is the expanded memory manager of Microsoft's MS-DOS, IBM's PC DOS, Digital Research's DR-DOS, and Datalight's ROM-DOS which is used to create expanded memory using extended memory on Intel 80386 CPUs. There also is an EMM386.EXE availabl ...
(GEMMIS)
*
x86 memory segmentation
x86 memory segmentation refers to the implementation of memory segmentation in the Intel x86 computer instruction set architecture. Segmentation was introduced on the Intel 8086 in 1978 as a way to allow programs to address more than 64 KB ...
*
Address Windowing Extensions
Address Windowing Extensions (AWE) is a Microsoft Windows application programming interface that allows a 32-bit software application to access more physical memory than it has virtual address space, even in excess of the 4 GB limit. The process of ...
(AWE)
*
Physical Address Extension
In computing, Physical Address Extension (PAE), sometimes referred to as Page Address Extension,
is a memory management feature for the x86 architecture. PAE was first introduced by Intel in the Pentium Pro, and later by AMD in the Athlon process ...
(PAE)
References
Further reading
*
*
* {{cite web , title=Understanding EMS 4.0 , author-first=Lloyd Robert , author-last=Borrett , work=Technical Cornucopia , date=January–February 1989 , url=http://www.borrett.id.au/computing/art-1989-01-02.htm , access-date=2020-02-08 , url-status=live , archive-url=https://web.archive.org/web/20200208213504/http://www.borrett.id.au/computing/art-1989-01-02.htm , archive-date=2020-02-08
X86 memory management
DOS memory management
Memory expansion