View source for Single address space operating system

{{Short description|Executive order}}
In [[Computer science|computer science]], a '''single address space operating system''' (or '''SASOS''') is an [[Operating system|operating system]] that provides only one globally shared [[Address space|address space]] for all [[Process (computing)|processes]]. In a single address space operating system, numerically identical ([[Virtual memory|virtual memory]]) [[Logical address|logical address]]es in different processes all refer to exactly the same byte of data.<ref>{{cite journal|journal=ACM SIGPLAN Notices|volume=27|issue=9|pages=175–186|date=September 1992|author1=Eric J. Koldinger|author2=Jeffrey S. Chase|author3=Susan J. Eggers|title=Architecture support for single address space operating systems|doi=10.1145/143371.143508}}</ref>

In a traditional OS with private per-process address space, memory protection is based on address space boundaries ("address space isolation"). Single address-space operating systems make translation and protection orthogonal, which in no way weakens protection.<ref name=Wil95>{{cite web |author1=Tim Wilkinson|author2=Kevin Murray|author3=Stephen Russell|author4=Gernot Heiser|author5=Jochen Liedt|title=Single Address Space Operating Systems |website=University of New South Wales |date=13 November 1995|url=https://cgi.cse.unsw.edu.au/~reports/papers/9504.pdf|citeseerx=10.1.1.13.7042|at=Section 2: "Memory Protection"}}</ref><ref name=Cha94>{{cite journal|author1=Jeffrey S. Chase|author2=Henry M. Levy|author3=Michael J. Feeley|author4=Edward D. Lazowska|author4-link=Edward D. Lazowska|url=https://homes.cs.washington.edu/~levy/opal/opal-tocs.pdf|title=Sharing and protection in a single-address-space operating system|journal=ACM Transactions on Computer Systems|volume=12|issue=4|pages=271–307|date=November 1994|doi=10.1145/195792.195795|citeseerx=10.1.1.127.7313}}</ref> 
The core advantage is that pointers (i.e. memory references) have global validity, meaning their meaning is independent of the process using it. This allows sharing pointer-connected data structures across processes, and making them persistent, i.e. storing them on backup store.

Some [[Instruction set architecture|processor architectures]] have direct support for protection independent of translation. On such architectures, a SASOS may be able to perform context switches faster than a traditional OS. Such architectures include [[Engineering:Itanium|Itanium]], and Version 5 of the [[ARM architecture family|Arm architecture]], as well as [[Capability-based addressing|capability architectures]] such as CHERI.

A SASOS should not be confused with a [[Flat memory model|flat memory model]], which provides no address translation and generally no memory protection. In contrast, a SASOS makes protection orthogonal to translation: it may be possible to name a data item (i.e. know its virtual address) while not being able to access it.

SASOS projects using hardware-based protection include the following:
* [https://www.doc.ic.ac.uk/~phjk/Publications/murray93design.pdf Angel] 
* [[Software:IBM i|IBM i]] (formerly called OS/400) 
* [http://www.ertos.nicta.com.au/iguana/ Iguana] at [[Organization:NICTA|NICTA]], Australia
* [http://www.ertos.nicta.com.au/research/mungi/ Mungi] at [[Organization:NICTA|NICTA]], Australia
* [http://www.cl.cam.ac.uk/Research/SRG/netos/old-projects/nemesis/ Nemesis]
* [http://www.cs.washington.edu/homes/levy/opal/opal.html Opal]
* [[Software:Scout (operating system)|Scout]]
* [http://www.eas.asu.edu/~sasos/ Sombrero]

Related are OSes that provide protection through language-level type safety
* [http://brix-os.sourceforge.net/?p0=info&p1=design&p2=arch-sassl Br1X] 
* [[Software:Genera (operating system)|Genera]]
* [[Software:JX (operating system)|JX]] a research Java OS<ref>{{cite web|url=http://www4.cs.fau.de/Projects/JX/publications/jx-usenix.pdf|title=The JX Operating System|author1=Michael Golm|author2=Meik Felser|author3=Christian Wawersich|author4=Jürgen Kleinöder}}</ref>
* [[Software:Phantom OS|Phantom OS]]
* [[Software:Singularity (operating system)|Singularity]]
* [https://github.com/theseus-os/Theseus Theseus OS]<ref>
Kevin Boos, Namitha Liyanage, Ramla Ijaz, and Lin Zhong.
[https://www.usenix.org/conference/osdi20/presentation/boos "Theseus: an Experiment in Operating System Structure and State Management"].
2020.
</ref>
* [http://www.torsion.org/ Torsion]<ref>
[http://www.nongnu.org/torsion/ "Torsion Operating System"].
quote: "Torsion ... a single address space multitasking operating system with transparent data persistence."
</ref>

== See also ==
* [[Software:Exokernel|Exokernel]]
*[[Software:Hybrid kernel|Hybrid kernel]]
*[[Software:Kernel (operating system)|Kernel]]
*[[Microkernel]]
*Nanokernel
*[[Software:Unikernel|Unikernel]]
*[[Flat memory model]]
*[[Virtual memory]]

== References ==
{{Reflist}}

== Bibliography ==
* {{cite journal|author=Jeffrey S. Chase|author2=Henry M. Levy|author3=Michael J. Feeley|author4=Edward D. Lazowska|author4-link=Edward D. Lazowska|title=Sharing and protection in a single-address-space operating system|journal=ACM Transactions on Computer Systems|volume=12|issue=4|pages=271–307|date=November 1994|doi=10.1145/195792.195795|citeseerx=10.1.1.127.7313}}. 
* {{cite journal
 | last1 = Heiser
 | first1 = Gernot
 | last2 = Elphinstone
 | first2 = Kevin
 | last3 = Vochteloo
 | first3 = Jerry
 | last4 = Russell
 | first4 = Stephen
 | last5 = Liedtke
 | first5 = Jochen
 | year = 1998
 | title = The Mungi Single-Address-Space Operating System
 | journal = Software: Practice and Experience
 | volume = 28
 | issue = 9
 | pages = 901&ndash;928
 | doi = 10.1002/(SICI)1097-024X(19980725)28:9<901::AID-SPE181>3.0.CO;2-7
 |citeseerx = 10.1.1.146.4216| s2cid = 62189930
 |url = http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.146.4216&rep=rep1&type=pdf
 |url-status = live
 |archive-date = June 27, 2022
 |archive-url = https://archive.today/20220627010816/http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.146.4216&rep=rep1&type=pdf
 }}
* {{cite journal|title=Improving the reliability of commodity operating systems|author=Michael M. Swift|author2=Brian N. Bershad|author3=Henry M. Levy|journal=ACM SIGOPS Operating Systems Review|doi=10.1145/1165389.945466|date=December 2003|volume=37|issue=5|page=207|citeseerx = 10.1.1.5.3338}}
* {{cite journal|title=Architecture support for single address space operating systems|author=Eric J. Koldinger|author2=Jeffrey S. Chase|author3=Susan J. Eggers|journal=ACM SIGPLAN Notices|doi=10.1145/143371.143508|volume=27|issue=9|pages=175–186|date=September 1992}}

[[Category:Operating systems]]



{{Sourceattribution|Single address space operating system}}