Editing L4 microkernel family (section)

{{Short description|Family of second-generation microkernels}}
{{Use dmy dates|date=June 2021}}
{{Infobox OS
| name = L4 microkernel family
| logo = <!-- Filename only: no wikilink, Image: or File: -->
| logo caption = 
| logo alt = 
| screenshot = <!-- Filename only: no wikilink, Image: or File: -->
| caption = 
| screenshot alt = 
| developer = [[Jochen Liedtke]]
| family = L4
| working state = Current
| source model = [[Open-source software|Open source]], [[closed source]]
| released = {{Start date and age|1993}}<!-- If known, add |mm|dd|df=yes -->
| latest release version = 
| latest release date = {{Start date and age|2020}}<!-- If known, add |mm|dd|df=yes -->
| repo = <!-- {{URL|https://example.com}} -->
| marketing target = Reliable computing
| programmed in = [[Assembly language]], then [[C (programming language)|C]], [[C++]]
| language = English, German
| language count = 
| update model = <!-- APT, Windows Update, etc. -->
| package manager = <!-- dpkg, rpm, Windows installer, etc. -->
| supported platforms = Intel [[i386]], [[x86]], [[x86-64]], [[ARM architecture|ARM]], [[MIPS architecture|MIPS]], [[SPARC]], [[Itanium]], [[RISC-V]]
| kernel type = [[Microkernel]]
| userland = 
| ui = 
| license = [[Source code]], [[Formal proof|proofs]]: [[GNU General Public License#Version 2|GPLv2]]<br/>[[Library (computing)|Libraries]], [[Programming tool|tools]]: [[BSD licenses#2-clause|BSD 2-clause]]
| preceded by = [[Eumel]]
| succeeded by = 
| website = {{URL|os.inf.tu-dresden.de/L4}}
| other articles = 
}}
'''L4''' is a family of second-generation [[microkernel]]s, used to implement a variety of types of [[operating system]]s (OS), though mostly for [[Unix-like]], ''Portable Operating System Interface'' ([[POSIX]]) compliant types.

L4, like its predecessor microkernel [[#L3|L3]], was created by [[Germany|German]] [[computer scientist]] [[Jochen Liedtke]] as a response to the poor performance of earlier microkernel-based OSes. Liedtke felt that a system designed from the start for high performance, rather than other goals, could produce a microkernel of practical use. His original implementation in hand-coded Intel [[i386]]-specific [[assembly language]] code in 1993 created attention by being 20 times faster than [[Mach (kernel)|Mach]].<ref name="Liedtke_93">{{cite conference
 |last=Liedtke |first=Jochen |author-link=Jochen Liedtke
 |title = Improving IPC by kernel design
 |book-title = 14th ACM Symposium on Operating System Principles
 |pages = 175–188
 |date=December 1993
 |location = Asheville, NC, USA
 |url = http://portal.acm.org/citation.cfm?id=168619.168633
}}</ref>
The follow-up publication two years later<ref name=Lie95>{{cite conference
 |last=Liedtke |first=Jochen |author-link=Jochen Liedtke
 |title = On μ-Kernel Construction
 |book-title = Proceedings 15th ACM Symposium on Operating Systems Principles (SOSP)
 |pages = 237–250
 |date = December 1995
 |url = http://os.itec.kit.edu/65_1029.php
 |archive-url = https://web.archive.org/web/20151025154932/http://os.itec.kit.edu/65_1029.php
 |archive-date = 25 October 2015
 |url-status = live}}</ref> was considered so influential that it won the 2015 [[ACM SIGOPS]] Hall of Fame Award.
Since its introduction, L4 has been developed to be [[Cross-platform software|cross-platform]] and to improve [[Computer security|security]], isolation, and [[Robustness (computer science)|robustness]].

There have been various re-implementations of the original L4 [[Kernel (operating system)|kernel]] [[application binary interface]] (ABI) and its successors, including ''L4Ka::Pistachio'' (implemented by Liedtke and his students at [[Karlsruhe Institute of Technology]]), ''L4/MIPS'' ([[University of New South Wales]] (UNSW)), ''Fiasco'' ([[Dresden University of Technology]] (TU Dresden)). For this reason, the name ''L4'' has been generalized and no longer refers to only Liedtke's original implementation. It now applies to the whole [[microkernel]] family including the L4 kernel [[Interface (computing)|interface]] and its different versions.

L4 is widely deployed. One variant, OKL4 from [[Open Kernel Labs]], shipped in billions of mobile devices.<ref name="OKL4 Microvisor">{{cite web |url=https://gdmissionsystems.com/cyber/products/trusted-computing-cross-domain/microvisor-products/ |title=Hypervisor Products: General Dynamics Mission Systems |website=General Dynamics Mission Systems |access-date=26 April 2018 |url-status=live |archive-url=https://web.archive.org/web/20171115152446/https://gdmissionsystems.com/cyber/products/trusted-computing-cross-domain/microvisor-products/ |archive-date=15 November 2017}}</ref><ref name=OKL_PR>
{{cite press release
 |title=Open Kernel Labs Software Surpasses Milestone of 1.5 Billion Mobile Device Shipments
 |url=http://www.ok-labs.com/releases/release/ok-labs-software-surpasses-milestone-of-1.5-billion-mobile-device-shipments
 |archive-url=https://web.archive.org/web/20120211210405/http://www.ok-labs.com/releases/release/ok-labs-software-surpasses-milestone-of-1.5-billion-mobile-device-shipments
 |archive-date=11 February 2012
 |url-status=dead
 |date=19 January 2012 |publisher=[[Open Kernel Labs]]
}}</ref>