science

Processor sharing

Processor sharing is a 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 Processor sharing rather than just read about it. In short: Processor sharing or egalitarian processor sharing is a service policy where the customers, clients or jobs are all served simultaneously, each receiving an equal fraction of the service capacity available. In such a system all jobs start service immediately (there is no queueing).

Key takeaways

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

Reference excerpt

Processor sharing or egalitarian processor sharing is a service policy where the customers, clients or jobs are all served simultaneously, each receiving an equal fraction of the service capacity available. In such a system all jobs start service immediately (there is no queueing). The processor sharing algorithm "emerged as an idealisation of round-robin scheduling algorithms in time-shared computer systems".

Queueing theory A single server queue operating subject to Poisson arrivals (such as an M/M/1 queue or M/G/1 queue) with a processor sharing discipline has a geometric stationary distribution. The sojourn time jobs experience has no closed form solution, even in an M/M/1 queue.

Generalized processor sharing

Generalized processor sharing is a multi-class adaptation of the policy which shares service capacity according to positive weight factors to all non-empty job classes at the node, irrespective of the number of jobs of each class present. Often it is assumed that the jobs within a class form a queue and that queue is served on a first-come, first-served basis, but this assumption is not necessary for many GPS applications. In processor scheduling, generalized processor sharing is "an idealized scheduling algorithm that achieves perfect fairness. All practical schedulers approximate GPS and use it as a reference to measure fairness."

Multilevel processor sharing In multilevel processor sharing a finite set of thresholds are defined and jobs partitioned according to how much service they have received. The lowest level (containing jobs which have received the least service) has the highest priority and higher levels monotonically decreasing priorities. Within each level an internal discipline is used.

References

Worked examples

Example 1 — a first encounter with Processor sharing

Start with the simplest possible case. Write down what Processor sharing claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In 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 Processor sharing 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 Processor sharing 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 Processor sharing

In research: Processor sharing appears in 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 Processor sharing 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: Processor sharing is common in secondary-school and first-year university syllabi. It links to neighbouring topics Queueing theory, so understanding it makes those chapters shorter.
In everyday life: Look for Processor sharing 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.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Processor sharing” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Processor sharing in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Processor sharing 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 Processor sharing out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Processor sharing in simple terms?

Why does Processor sharing matter?

Because it connects several 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 Processor sharing?

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 Processor sharing.