computer science

Single address space operating system

Single address space operating system is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Single address space operating system rather than just read about it. In short: 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.

Key takeaways

Single address space operating system belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Single address space operating system to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Single address space operating system from memory before moving on to harder problems.

Reference excerpt

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. 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, 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 Phantom OS Singularity Theseus OS Torsion

See also Exokernel Hybrid kernel Kernel Microkernel Nanokernel Unikernel Flat memory model Virtual memory

References

Bibliography Jeffrey S. Chase; Henry M. Levy; Michael J. Feeley; Edward D. Lazowska (November 1994). "Sharing and protection in a single-address-space operating system". ACM Transactions on Computer Systems. 12 (4): 271–307. CiteSeerX 10.1.1.127.7313. doi:10.1145/195792.195795. {{cite journal}}: Cite uses deprecated parameter |citeseerx= (help). Heiser, Gernot; Elphinstone, Kevin; Vochteloo, Jerry; Russell, Stephen; Liedtke, Jochen (1998). "The Mungi Single-Address-Space Operating System". Software: Practice and Experience. 28 (9): 901–928. CiteSeerX 10.1.1.146.4216. doi:10.1002/(SICI)1097-024X(19980725)28:9<901::AID-SPE181>3.0.CO;2-7. S2CID 62189930. Archived from the original on 2022-06-27. {{cite journal}}: Cite uses deprecated parameter |citeseerx= (help)CS1 maint: miscellaneous url (link) Michael M. Swift; Brian N. Bershad; Henry M. Levy (December 2003). "Improving the reliability of commodity operating systems". ACM SIGOPS Operating Systems Review. 37 (5): 207. CiteSeerX 10.1.1.5.3338. doi:10.1145/1165389.945466. {{cite journal}}: Cite uses deprecated parameter |citeseerx= (help) 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.

Worked examples

Example 1 — a first encounter with Single address space operating system

Start with the simplest possible case. Write down what Single address space operating system claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Single address space operating system before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Single address space operating system ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Single address space operating system

In research: Single address space operating system appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Single address space operating system in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Single address space operating system is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computer engineering stubs, Operating systems, so understanding it makes those chapters shorter.
In everyday life: Look for Single address space operating system outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Single address space operating system in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Single address space operating system means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Single address space operating system out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Single address space operating system in simple terms?

Why does Single address space operating system matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Single address space operating system?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Single address space operating system.