In computer science, a single address space operating system (or SASOS) is an operating system that provides only one globally shared

address space In computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral device, disk sector, a memory cell or other logical or physical entity. For software programs to save and retrieve st ...

for all

processes A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management *Business process, activities that produce a specific se ...

. In a single address space operating system, numerically identical ( virtual memory) logical addresses in different processes all refer to exactly the same byte of data. 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. 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 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 Itanium, and Version 5 of the

Arm architecture ARM (stylised in lowercase as arm, formerly an acronym for Advanced RISC Machines and originally Acorn RISC Machine) is a family of reduced instruction set computer (RISC) instruction set architectures for computer processors, configured ...

, as well as capability architectures such as CHERI. A SASOS should not be confused with a 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:
Angel
*

IBM i IBM i (the ''i'' standing for ''integrated'') is an operating system developed by IBM for IBM Power Systems. It was originally released in 1988 as OS/400, as the sole operating system of the IBM AS/400 line of systems. It was renamed to i5/OS in ...

(formerly called OS/400)
Iguana
at NICTA, Australia
Mungi
at NICTA, Australia
Nemesis

*

Scout Scout may refer to: Youth movement *Scout (Scouting), a child, usually 10–18 years of age, participating in the worldwide Scouting movement **Scouts (The Scout Association), section for 10-14 year olds in the United Kingdom **Scouts BSA, sectio ...

Sombrero
Related are OSes that provide protection through language-level type safety
Br1X
*

Genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

* JX a research Java OS * Phantom OS * Singularity
Theseus OS

Torsion
ref
"Torsion Operating System"
quote: "Torsion ... a single address space multitasking operating system with transparent data persistence."

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* . * * * Operating systems {{comp-eng-stub

See also

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Bibliography