View source for Software:EMM386

{{Infobox software
| name                   = EMM386
| logo                   =
| screenshot             =
| screenshot size        =
| caption                =
| developer              = [[Company:Microsoft|Microsoft]], [[Company:IBM|IBM]], [[Company:Digital Research|DR]], [[Software:Datalight|Datalight]], The FreeDOS team
| released               = {{Release year|df=yes|1988}}
| latest release version =
| latest release date    =
| operating system       = [[Software:MS-DOS|MS-DOS]], [[Software:IBM PC DOS|PC DOS]], [[Software:DR DOS|DR DOS]], [[ROM-DOS]], [[Software:FreeDOS|FreeDOS]]
| platform               = [[Engineering:Intel 80386|Intel 80386]]
| genre                  = [[Expanded memory]] manager, [[Command (computing)|Command]]
| license                =
| website                =
}}
'''EMM386''' is the [[Expanded memory|expanded memory]] manager of [[Company:Microsoft|Microsoft]]'s [[Software:MS-DOS|MS-DOS]], [[Company:IBM|IBM]]'s [[Software:PC DOS|PC DOS]], [[Company:Digital Research|Digital Research]]'s [[Software:DR-DOS|DR-DOS]], and [[Software:Datalight|Datalight]]'s [[ROM-DOS]]<ref>{{Cite web|url=https://www.datalight.com/assets/files/ROM-DOS_Users_Guide.pdf|title=Datalight ROM-DOS User's Guide|website=www.datalight.com}}</ref> which is used to create expanded memory using [[Extended memory|extended memory]] on [[Engineering:Intel 80386|Intel 80386]] CPUs. There also is an EMM386.EXE available in [[Software:FreeDOS|FreeDOS]].<ref name="Platt_2003_EMM386"/>

==Overview==
EMM386.EXE can map memory into unused blocks in the [[Upper memory area|upper memory area]] (UMA), allowing device drivers and [[Terminate-and-stay-resident program|terminate-and-stay-resident program]]s to be "loaded high", preserving [[Conventional memory|conventional memory]].

The technique probably first appeared with the development of CEMM, included with Compaq's OEM [[Software:MS-DOS|MS-DOS]] for the Compaq Deskpro 386 in 1986. Microsoft's version first appeared, built-in, with Windows/386 2.0 in 1987 and as standalone EMM386.SYS with MS-DOS 4.0 in 1988; the more flexible EMM386.EXE version appeared in MS-DOS 5.0 in 1991.

EMM386 uses the processor's [[Virtual 8086 mode|virtual 8086 mode]]. This forces memory accesses made by DOS applications to go through the processor's [[Memory management unit|MMU]] (introduced in the 386), and the page table entries used by the MMU are configured by EMM386 to map certain regions in upper memory to areas of extended memory (obtained by EMM386 through the extended memory manager [[HIMEM.SYS]]). This technique enabled both EMS (expanded memory) as well as UMBs - both of which appear to DOS applications to be memory in the upper area but are in fact mapped to physical memory locations beyond 1MB.

It temporarily shuts down during a Windows session in ''386 Enhanced'' mode, with Windows' [[Protected mode|protected mode]] kernel taking over its role.

Windows uses the GEMMIS API to take over memory management from EMM386.EXE. '''Global EMM Import Specification''' (GEMMIS) is supported via a document available to a select number of memory-manager vendors ("Windows/386 Paging Import Specification").<ref name="Okazaki_1994_GEMMIS"/><ref name="Brown_1994"/><ref name="Lespinasse"/><ref name="Paul_2002_HMA7"/>

Only a few memory managers implemented the GEMMIS API, some of the ones that include it are: EMM386.EXE, Quarterdeck QEMM, Qualitas 386MAX, [[Software:Helix Netroom|Helix Netroom]]<ref name="Okazaki_1994_GEMMIS"/> and DOSBox builtin DOS. Notably missing are FreeDOS's memory managers.

None of the FreeDOS memory managers (HIMEMX.EXE, JEMM386.EXE, JEMMEX.EXE) implement the GEMMIS API and Windows fails to start when running in conjunction with JEMMxxx since Windows fails to take over the memory management role. Windows ME, [[Software:Windows 98|Windows 98]], [[Software:Windows 95|Windows 95]], Windows for Workgroups 3.1x, and Windows 3.xx, all will fail with JEMMxxx displaying:

  Cannot run Windows while the currently installed protected-mode software is
  running.

  Quit the protected-mode software, and then try again.
  You may need to restart your computer.

With JEMMxx, it is possible to run Windows 3.x and Windows for Workgroups 3.1x in limited capabilities by forcing Windows to use Standard Mode; i.e. using 80286 Protected Mode, not 80386 Enhanced Mode.  Three conditions are required:
# limit total XMS to 64MB
# EMS must be enabled, can't use NOEMS option.  For example JEMMEX X2MAX=65422
# Windows operate in Standard Mode only, WIN /S or WIN /2
Note that Windows in standard mode is limited in functionality, it lacks virtual memory, it skips the [386Enh] section in SYSTEM.INI and any device drivers in [386Enh] are not loaded.

==History==
{| class="wikitable"
|+ EMM386 Version history<ref>{{cite web | url=https://www.infania.net/ms6kb/Q98768.htm | title=Q98768 - Troubleshooting MS-DOS 6.x and EMM386.EXE }}</ref><ref>{{cite web | url=https://hwiegman.home.xs4all.nl/msdos/78557.htm | title=EMM386 Troubleshooting and Technical Information (78557) }}</ref><ref>{{cite web | url=https://hwiegman.home.xs4all.nl/msdos/74977.htm | title=EMM386 and Early Versions of HIMEM.SYS (74977) }}</ref>
|-
! Bundled with !! Date !! Filename !! Version
|-
| [[Software:MS-DOS#4.01|MS-DOS 4.01]] || November 1988 || EMM386.SYS || 4.00
|-
| [[Software:Windows 3.0|Windows 3.0]] || May 1990 || EMM386.SYS || 4.10.0419
|-
| [[Software:MS-DOS#5.00|MS-DOS 5.0]] || June 1991 || EMM386.EXE || 4.20.06x
|-
| [[Software:IBM PC DOS|IBM PC DOS 5.0]] || June 1991 || EMM386.EXE || 4.20.06x
|-
| [[Software:IBM PC DOS#PC DOS 5|IBM PC DOS 5.02]] || September 1992 || EMM386.EXE || 4.33
|-
| MS-DOS 5.00a || November 1992 || EMM386.EXE || 4.33
|-
| [[Software:Windows 3.1x|Windows 3.1]] || April 1992 || EMM386.EXE || 4.44
|-
| [[Software:Windows 3.1x#Windows for Workgroups 3.1|Windows for Workgroups 3.1]] || October 1992 || EMM386.EXE || 4.44
|-
| [[Software:MS-DOS#6.00|MS-DOS 6.0]] || March 1993 || EMM386.EXE || 4.45
|-
| [[Software:IBM PC DOS#PC DOS 6.1|IBM PC DOS 6.1]] || June 1993 || EMM386.EXE || 4.45
|-
| [[Software:MS-DOS#6|MS-DOS 6.2]] || September 1993 || EMM386.EXE || 4.48
|-
| Windows 3.11 || November 1993 || EMM386.EXE || 4.48
|-
| [[Software:Windows 3.1x#Windows for Workgroups 3.11|Windows for Workgroups 3.11]] || November 1993 || EMM386.EXE || 4.48
|-
| MS-DOS 6.21 || March 1994 || EMM386.EXE || 4.48
|-
| [[Software:IBM PC DOS#PC DOS 6.3|IBM PC DOS 6.3]] || April 1994 || EMM386.EXE || 4.48
|-
| [[Software:MS-DOS#6"|MS-DOS 6.22]] || June 1994 || EMM386.EXE || 4.49
|-
| [[Software:IBM PC DOS#PC DOS 7|IBM PC DOS 7.0]] || April 1995 || EMM386.EXE || 4.50
|-
| [[Software:IBM PC DOS#PC DOS 2000|IBM PC DOS 2000]] || May 1998 || EMM386.EXE || 4.50
|-
| [[Software:Windows 95|Windows 95]] || August 1995 || EMM386.EXE || 4.95
|-
| [[Software:Windows 98|Windows 98]] || June 1998 || EMM386.EXE || 4.95
|}

==See also==
* [[Upper memory area]] (UMA)
* [[Extended memory]] (XMS)
* [[Expanded memory]] (EMS)
* [[List of DOS commands]]

==References==
{{reflist|refs=
<ref name="Platt_2003_EMM386">{{cite web |title=Command: EMM386 |author-first1=Robert |author-last1=Platt |author-first2=W. |author-last2=Spiegl |date=2008 |orig-year=2003 |url=http://help.fdos.org/en/hhstndrd/base/emm386.htm |access-date=2015-10-21 |url-status=live |archive-url=https://web.archive.org/web/20170823174504/http://help.fdos.org/en/hhstndrd/base/emm386.htm |archive-date=2017-08-23}}</ref>
<ref name="Brown_1994">{{cite journal |title=QPI: The QEMM-386 Programming Interface |author-first1=Ralf D. |author-last1=Brown |author-first2=Andrew |author-last2=Schulman |series=Undocumented Corner |date=July 1994 |journal=Dr. Dobb's Journal |location=San Mateo, California |pages=123–131 |url=https://www.cs.cmu.edu/~ralf/papers/qpi.txt |access-date=2017-08-23 |url-status=live |archive-url=https://web.archive.org/web/20170823173501/https://www.cs.cmu.edu/~ralf/papers/qpi.txt |archive-date=2017-08-23}}</ref>
<ref name="Okazaki_1994_GEMMIS">{{cite journal |title=The Windows Global EMM Import Interface |author-first1=Taku |author-last1=Okazaki |author-first2=Andrew |author-last2=Schulman |series=Undocumented Corner |date=1994-09-01 |issue=9 |journal=Dr. Dobb's Journal |url=http://www.drdobbs.com/windows/undocumented-corner/184409317 |access-date=2015-10-21 |url-status=live |archive-url=https://web.archive.org/web/20170823174701/http://www.drdobbs.com/windows/undocumented-corner/184409317 |archive-date=2017-08-23 }} [http://collaboration.cmc.ec.gc.ca/science/rpn/biblio/ddj/Website/articles/DDJ/1994/9409/9409m/9409m.htm] {{Webarchive|url=https://archive.today/20140529185309/http://collaboration.cmc.ec.gc.ca/science/rpn/biblio/ddj/Website/articles/DDJ/1994/9409/9409m/9409m.htm |date=2014-05-29 }} [https://web.archive.org/web/20170823174853/http://www.drdobbs.com/windows/undocumented-corner/windows/sourcecode/undocumented-corner/30400554] [https://web.archive.org/web/20170823175353/http://www.drdobbs.com/windows/undocumented-corner/windows/sourcecode/undocumented-corner/30400553]</ref>
<ref name="Lespinasse">{{cite web |title=How to kick out a memory manager |author-first=Michel |author-last=Lespinasse |publisher=Walken / Impact Studios |location=Amiens, France |url=http://dgi_il.tripod.com/gemmis.txt |access-date=2015-10-21 |url-status=live |archive-url=https://web.archive.org/web/20170104093930/http://dgi_il.tripod.com/gemmis.txt |archive-date=2017-01-04}}</ref>
<ref name="Paul_2002_HMA7">{{cite newsgroup |title=Suche freien Speicherbereich unterhalb von 1 MB, der nicht von OS überschrieben wird |author-first=Matthias R. |author-last=Paul |date=2002-08-13 |newsgroup=de.comp.lang.assembler.x86 |language=de |url=https://groups.google.com/d/msg/de.comp.lang.assembler.x86/boKnIpqPl-Q/ZLDFDX9E1e0J |access-date=2017-09-03 |url-status=live |archive-url=https://archive.today/20170904001428/https://groups.google.com/forum/%23!msg/de.comp.lang.assembler.x86/boKnIpqPl-Q/ZLDFDX9E1e0J |archive-date=2017-09-04}}</ref>
}}

{{DEFAULTSORT:Emm386}}
[[Category:DOS memory management]]


{{Sourceattribution|EMM386|1}}