In computer science, a single address space operating system (or SASOS) is an operating system that provides only one globally shared address space for all processes. 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.[1]
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.[2][3]
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, 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 (formerly called OS/400)
Iguana at NICTA, Australia
Mungi at NICTA, Australia
Nemesis
Opal
Scout
Sombrero
Related are OSes that provide protection through language-level type safety
Br1X
Genera
JX a research Java OS[4]
Phantom OS
Singularity
Theseus OS[5]
Torsion[6]
^Eric J. Koldinger; Jeffrey S. Chase; Susan J. Eggers (September 1992). "Architecture support for single address space operating systems". ACM SIGPLAN Notices. 27 (9): 175–186. doi:10.1145/143371.143508.
^Tim Wilkinson; Kevin Murray; Stephen Russell; Gernot Heiser; Jochen Liedt (13 November 1995). "Single Address Space Operating Systems" (PDF). University of New South Wales. Section 2: "Memory Protection". CiteSeerX 10.1.1.13.7042.
^Jeffrey S. Chase; Henry M. Levy; Michael J. Feeley; Edward D. Lazowska (November 1994). "Sharing and protection in a single-address-space operating system" (PDF). ACM Transactions on Computer Systems. 12 (4): 271–307. CiteSeerX 10.1.1.127.7313. doi:10.1145/195792.195795.
^Michael Golm; Meik Felser; Christian Wawersich; Jürgen Kleinöder. "The JX Operating System" (PDF).
^
Kevin Boos, Namitha Liyanage, Ramla Ijaz, and Lin Zhong.
"Theseus: an Experiment in Operating System Structure and State Management".
2020.
^
"Torsion Operating System".
quote: "Torsion ... a single address space multitasking operating system with transparent data persistence."
and 24 Related for: Single address space operating system information
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