Windows on Windows: Difference between revisions

Revision as of 16:31, 4 October 2018

Revision as of 22:56, 23 June 2019

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{{About|the 16-bit subsystem in the 32-bit editions of Windows NT|the 32-bit compatibility layer in the 64-bit editions|WoW64}}

{{Infobox software

| name = Windows on Windows

| screenshot =

| screenshot_size =

| caption =

| other_names = WOW

| developer = [[Microsoft]]

| released =

| replaces =

| operating system = [[Microsoft Windows]]

| genre = [[Compatibility layer]]

}}

In [[computing]], '''Windows on Windows''' (commonly referred to as '''WOW''',<ref>{{cite web|url=http://support.microsoft.com/kb/181333|title=WOW Environment Remains in Memory After Quitting 16-Bit Program|website=Support|publisher=[[Microsoft]]|accessdate=February 7, 2017|date=February 22, 2007|deadurl=yes|archiveurl=https://web.archive.org/web/20071023060218/http://support.microsoft.com/kb/181333|archivedate=October 23, 2007}}</ref><ref>{{cite web|url=http://support.microsoft.com/kb/153544|title=Starting 16-Bit WOW Subsystem on Windows NT Server|date=November 1, 2016|accessdate=February 7, 2017|website=Support|publisher=[[Microsoft]]|deadurl=yes|archiveurl=https://web.archive.org/web/20070509051612/http://support.microsoft.com/kb/153544|archivedate=May 9, 2007}}</ref><ref>{{cite web|url=https://support.microsoft.com/kb/220159|title=Disabling the MSDOS and WOWEXEC Subsystems on Terminal Server|date=November 1, 2006|website=Support|publisher=[[Microsoft]]|accessdate=February 7, 2017|deadurl=no|archiveurl=https://web.archive.org/web/20080113000651/http://support.microsoft.com/kb/220159|archivedate=November 30, 2008}}</ref>) is a [[compatibility layer]] of [[32-bit]] versions of the Microsoft [[Windows NT]] family of [[operating system]]s that extends [[Virtual DOS machine#Windows NTVDM|NTVDM]] to provide limited support for running [[legacy code|legacy]] [[16-bit]] programs written for [[Windows 3.x]] or earlier. There is a similar subsystem, known as [[WoW64]], on 64-bit Windows versions that runs 32-bit programs.

== Background ==

Many 16-bit Windows legacy programs can run without changes on newer [[32-bit]] editions of Windows. The reason designers made this possible was to allow software developers time to remedy their software during the industry transition from [[Windows 3.1x]] to [[Windows 95]] and later, without restricting the ability for the operating system to be upgraded to a current version before ''all'' programs used by a customer had been taken care of.

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A considerable number of shims are present in the [[compatibility layer|application compatibility layer]] of later versions of Windows to intercept and modify [[Application programming interface|API]] calls made by legacy applications that were written with a different set of assumptions and operating system best practices in mind.<ref>{{cite web|website=TechNet|publisher=[[Microsoft]]|url=https://technet.microsoft.com/en-us/library/ee461265(v=ws.10).aspx|title=Application Compatibility|accessdate=February 7, 2017}}</ref> These fixes are updated from time-to-time as issues are discovered in popular legacy applications that are still in use.<ref>{{cite web|url=http://support.microsoft.com/kb/2272691|title=Application Compatibility Update for Windows 7 and Windows Server 2008 R2: August 2010|website=Support|publisher=[[Microsoft]]|accessdate=February 7, 2017|date=August 24, 2010}}</ref>

== See also ==

* [[Wine (software)]]

==References==

{{reflistReflist}}

== External links ==

* [http://www.microsoft.com/technet/archive/winntas/training/ntarchitectoview/ntarc_5.mspx?mfr=true Windows NT subsystems]

* [http://kb.iu.edu/data/acxn.html What are NTVDM and WOW?]