Editing Compatibility layer (section)

==Software==

Examples include:

* [[Wine (software)|Wine]], which runs some [[Microsoft Windows]] binaries on [[Unix-like]] systems using a program loader and the [[Windows API]] implemented in DLLs
* [[Microsoft Windows|Windows]]'s application compatibility layers to attempt to run poorly written applications or those written for earlier versions of the platform.<ref>
{{cite web|url=https://docs.microsoft.com/en-us/windows/win32/win7appqual/application-compatibility-toolkit--act-|title=Application Compatibility in Windows XP|author=Charlie Russel, Microsoft MVP for Windows Server and Tablet PC|date=2002-02-18}}
</ref>
* [[LINA (software)|Lina]], which runs some Linux binaries on Windows, [[Mac OS X]] and Unix-like systems with native look and feel.
* KernelEX, which runs some Windows 2000/XP programs on Windows 98/Me.
* [[Executor (software)|Executor]], which runs 68k-based "classic" Mac OS programs in Windows, Mac OS X and Linux.
* [[Anbox]], an [[Android (operating system)|Android]] compatibility layer for [[Linux]].
* [[Hybris (software)|Hybris]], library that translates Bionic into glibc calls.
* [[Darling (software)|Darling]], a translation layer that attempts to run Mac OS X and Darwin binaries on Linux.
* [[Windows Subsystem for Linux]] v1, which runs Linux binaries on Windows via a compatibility layer which translates Linux system calls into native windows system calls.
*[[Cygwin]], a [[POSIX]]-compatible environment that runs natively on Windows.<ref>{{Cite web|url=https://www.cygwin.com/|title=Cygwin|website=www.cygwin.com|access-date=2019-11-23}}</ref>
* [[2ine]], a project to run [[OS/2]] application on Linux<ref>{{Cite web|url=https://www.patreon.com/posts/project-2ine-16513790|title=Project: 2ine &#124; Patreon}}</ref>
* [[Rosetta 2]], [[Apple Inc.|Apple]]'s translation layer bundled with macOS Big Sur to allow x86-64 exclusive applications to run on ARM hardware.
* Prism is a [[Microsoft]] emulator for ARM-powered Windows devices that translates the underlying code of software built for traditional x86 and x64 binaries from [[Windows 11, version 24H2|Windows 11 24H2]]<ref>{{Cite web |last=mattwojo |date=2024-06-18 |title=How emulation works on Arm |url=https://learn.microsoft.com/en-us/windows/arm/apps-on-arm-x86-emulation |access-date=2024-11-26 |website=learn.microsoft.com |language=en-us}}</ref>
* ACL allows Android apps to natively execute on Tizen, webOS, or MeeGoo phones.<ref>{{Cite web | url=https://www.engadget.com/2012-05-15-tizen-os-android-apps.html | title=Tizen OS will run Android apps -- with a little help from third-party software (Video) | date=15 May 2012 }}</ref><ref>{{cite web | url=https://www.engadget.com/2013-04-28-openmobile-acl-for-webos-resurrected-on-kickstarter.html | title=OpenMobile ACL for webOS resurrected on Kickstarter, hopes to bring Android apps to HP Touchpad | date=29 April 2013 }}</ref><ref>{{cite web | url=https://www.engadget.com/2011-09-22-openmobile-demos-acl-for-meego-promises-100-compatibility-with.html | title=OpenMobile demos ACL for MeeGo, promises 100 percent compatibility with Android apps (Video) | date=22 September 2011 }}</ref>
* Alien Dalvik allows Android apps to run on MeeGo<ref>{{cite web | url=https://www.engadget.com/2011-02-08-myriad-alien-dalvik-runs-android-apps-on-any-phone-starting.html | title=Myriad 'Alien Dalvik' runs Android apps on any phone... Starting with MeeGo (Video) | date=8 February 2011 }}</ref> and Meamo.<ref>{{cite web | url=https://www.engadget.com/2011-02-18-myriad-alien-dalvik-hands-on-video.html | title=Myriad Alien Dalvik hands-on (Video) | date=18 February 2011 }}</ref> Alien Dalvik 2.0 was also revealed for iOS on an iPad, however unlike MeeGo and Meamo, this version ran from the cloud.<ref>{{cite web | url=https://www.youtube.com/watch?v=0_Q-pVrYjis | title=Running Android Apps on the iPad with Myriad's Alien Dalvik | website=[[YouTube]] | date=20 October 2011 }}</ref><ref>{{cite web | url=https://www.engadget.com/2011-10-10-hands-on-with-myriads-alien-dalvik-2-0-on-an-ipad-video.html | title=Hands-on with Myriad's Alien Dalvik 2.0 on an iPad (Video) | date=10 October 2011 }}</ref><ref>{{cite web | url=https://www.cnet.com/tech/services-and-software/android-apps-to-run-on-ipad-with-alien-dalvik-2-0/ | title=Android apps to run on iPad with Alien Dalvik 2.0 }}</ref>
* [[touchHLE]] is a compatibility layer (referred to as a “high-level emulator”) for Windows and macOS made by Andrea "hikari_no_yume" (Sweden) in early 2023 to run legacy 32-bit iOS software. The compatibility layer was only able to run one software, [[Super Monkey Ball]] as of version 0.1.0. As of version 0.1.2, support for the Lite version of Super Monkey Ball, as well as [[Crash Bandicoot Nitro Kart 3D]] and ''Touch & Go'' has been added.<ref>{{cite web | url=https://github.com/hikari-no-yume/touchHLE/blob/trunk/APP_SUPPORT.md | title=TouchHLE: High-level emulator for iPhone OS apps | website=[[GitHub]] }}</ref> She says that fans will have to "be patient" for anything else to emulate. It uses code translation along with CPU emulation when necessary, and specifically stated that she does not want to be compatible with 64 bit software.<ref>{{cite web | url=https://www.techspot.com/news/97504-high-level-ios-emulator-touchhle-aims-preserve-old.html | title=High-level iOS emulator touchHLE runs on Windows and Mac, aims to preserve old iOS gaming apps | date=6 February 2023 }}</ref> Later a pull request to add support for Android was issued, which allowed Android devices to run Super Monkey Ball for iOS.<ref>{{cite web | url=https://9to5mac.com/2023/04/24/ios-emulator-to-android/ | title=Developer ports iOS emulator to Android, but you shouldn't get excited about it | work=9to5Mac | date=24 April 2023 | last1=Espósito | first1=Filipe }}</ref>
* ipasim is a compatibility layer for Windows that uses WinObjC to translate code from Objective C to native Windows code.<ref>{{cite web | url=http://hdl.handle.net/20.500.11956/108316 | hdl=20.500.11956/108316 | title=IOS emulator for Windows | date=27 June 2019 | last1=Joneš | first1=Jan }}</ref>
* aah (sic) is a program for macOS to run iOS apps on macOS 10.15 "Catalina" on x86 processors via translation of the programs via the [[Catalyst]] framework.<ref>{{cite web | url=https://github.com/zydeco/aah | title=Aah | website=[[GitHub]] }}</ref>
* brs-emu is a compatibility layer to run Roku software via BrightScript on other platforms: Web, Windows, macOS, and Linux.<ref>{{cite web | url=https://github.com/lvcabral/brs-emu | title=BRS-EMU: BrightScript Emulator | website=[[GitHub]] }}</ref>

Compatibility layer in [[Kernel (operating system)|kernel]]:
* [[FreeBSD#OS compatibility layers|FreeBSD's Linux compatibility layer]], which enables binaries built specifically for [[Linux]] to run on [[FreeBSD]]<ref>{{cite web
| url = http://www.freebsd.org/doc/en/articles/linux-emulation/index.html
| title = Linux emulation in FreeBSD
}}
</ref> the same way as the native FreeBSD API layer.<ref>{{cite web|url=http://www.freebsd.org/doc/en/articles/linux-emulation/freebsd-emulation.html|title=Emulation|publisher=freebsd.org|access-date=2014-03-16}}</ref> FreeBSD also has some Unix-like system emulations, including NDIS, NetBSD, PECoff, SVR4, and different CPU versions of FreeBSD.<ref>{{cite web|url=http://www.freebsd.org/doc/en/articles/linux-emulation/inside.html|title=A look inside...|publisher=freebsd.org|access-date=2014-03-16}}</ref>
* [[NetBSD]] has several Unix-like system emulations.<ref>{{cite web|url=http://www.netbsd.org/docs/compat.html|title=NetBSD Binary Emulation|publisher=netbsd.org|access-date=2014-03-16}}</ref>
* [[Columbia Cycada]], an unreleased compatibility layer which runs [[IOS|Apple iOS]] applications on [[Android (operating system)|Android]] systems
* [[Windows Subsystem for Linux]] provides a [[Linux]]-compatible kernel interface developed by Microsoft.<ref>{{Cite web|url=https://docs.microsoft.com/en-us/windows/wsl/compare-versions#whats-new-in-wsl-2|title = Comparing WSL 1 and WSL 2| date=20 March 2023 }}</ref>
* [https://web.archive.org/web/20081015065906/http://chiharu.haun.org/peace/ The PEACE Project] (aka COMPAT_PECOFF) has Win32 compatible layer for NetBSD. The project is now inactive.<!--
UnifiedKernel sets the Windows system calls into kernel. it doesn't need translate system calls. UnifiedKernel is a kernel not a layer.
** [[Linux Unified Kernel]], which runs Windows binaries on patched Linux with kernel level support.

-->
* On [[RSTS/E]] for the [[PDP-11]] series of [[minicomputer]]s, programs written to run on the [[RT-11]] operating system could run (without recompiling) on RSTS through the RT-11 Run-Time System having its EMT flag set, meaning that an RT-11 [[System call|EMT instruction]] that matches a RSTS EMT is diverted to the RT-11 Run-Time System which translates them to the equivalent RSTS EMT. Programs written to take advantage of RSTS directly (or calls to RSTS within the Run-Time system itself) signal this by having a ''second'' EMT instruction (usually EMT 255) immediately before the actual RSTS EMT code.

<!-- this isn't laundry list time; give enough examples to give the idea, not the entire category-->
A compatibility layer avoids both the complexity and the speed penalty of full hardware [[emulator|emulation]]. Some programs may even run faster than the original, ''e.g.'' some Linux applications running on FreeBSD's Linux compatibility layer may perform better than the same applications on Red Hat Linux. Benchmarks are occasionally run on Wine to compare it to Windows NT-based operating systems.<ref>[http://wiki.winehq.org/BenchMark-0.9.5 BenchMark-0.9.5] {{Webarchive|url=https://web.archive.org/web/20101209221003/http://wiki.winehq.org/BenchMark-0.9.5 |date=2010-12-09 }} - The Official Wine Wiki</ref>

Even on similar systems, the details of implementing a compatibility layer can be quite intricate and troublesome; a good example is the [[IRIX]] binary compatibility layer in the [[MIPS architecture]] version of [[NetBSD]].<ref>{{cite web
| url = http://www.onlamp.com/pub/a/bsd/2002/08/08/irix.html
| title = IRIX Binary Compatibility, Part 1
| date = August 8, 2002
| author = Emmanuel Dreyfus
| publisher = onlamp.com
| access-date = 2014-03-16 <!--comment = detailed description of practical issues in compatibility layer implementation-->
| archive-date = 2017-10-21
| archive-url = https://web.archive.org/web/20171021211722/http://www.onlamp.com/pub/a/bsd/2002/08/08/irix.html
| url-status = dead
}}</ref>

A compatibility layer requires the host system's [[Central processing unit|CPU]] to be (upwardly) [[Computer compatibility|compatible]] to that of the foreign system. For example, a Microsoft Windows compatibility layer is not possible on [[PowerPC]] hardware because Windows requires an [[x86]] CPU. In this case full emulation is needed.