computer science

Pollack's rule

Pollack's rule 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 Pollack's rule rather than just read about it. In short: Pollack's Rule states that microprocessor "performance increase due to microarchitecture advances is roughly proportional to [the] square root of [the] increase in complexity". This contrasts with power consumption increase, which is roughly linearly proportional to the increase in complexity.

Key takeaways

Pollack's rule 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 Pollack's rule to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Pollack's rule from memory before moving on to harder problems.

Reference excerpt

Pollack's Rule states that microprocessor "performance increase due to microarchitecture advances is roughly proportional to [the] square root of [the] increase in complexity". This contrasts with power consumption increase, which is roughly linearly proportional to the increase in complexity. Complexity in this context means processor logic, i.e. its area. The rule, which is an industry term, is named for Fred Pollack, a lead engineer and fellow at Intel. Pollack's Rule gained increasing relevance in 2008 due to the broad adoption of multi-core computing and concern expressed by businesses and individuals at the huge electricity demands of computers. A generous interpretation of the rule allows for the case in which an ideal device could contain hundreds of low-complexity cores, each operating at very low power and together performing large amounts of (processing) work quickly. This describes a massively parallel processor array (MPPA), which is currently being used in embedded systems and hardware accelerators. However, Pollack's Law as originally formulated was considered to be a limit on the performance improvements for single CPUs as the number of transistors increased, as well as for multiprocessor systems.

Implications of the rule on chip performance According to Moore's law, each new technology generation doubles number of transistors. This increases their speed by 40%. On the other hand, Pollack's rule implies that microarchitecture advances improve the performance by another √2 ≈ 41%. Therefore, the overall performance increase is roughly two-fold, while the power consumption stays the same. In practice, however, implementing new microarchitecture every new generation is difficult, so microarchitecture gains are typically less.

References

External links Borkar, Shekhar. "Thousand Core Chips - A Technology Perspective" (PDF). Archived from the original (PDF) on 2012-02-13. Retrieved 2008-06-01. Beachler, Bob (Aug–Sep 2007). "New Multicore Architectures Face Substantial Challenges". Chip Design. Retrieved 2008-06-01. Crepps, Bob; Garver, Shu-ling (Aug 9, 2006). "The New Era of Tera-scale Computing".

Worked examples

Example 1 — a first encounter with Pollack's rule

Start with the simplest possible case. Write down what Pollack's rule 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 Pollack's rule 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 Pollack's rule 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 Pollack's rule

In research: Pollack's rule 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 Pollack's rule 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: Pollack's rule is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computer architecture statements, Electronic design, Microcomputer stubs, so understanding it makes those chapters shorter.
In everyday life: Look for Pollack's rule 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 “Pollack's rule” →

Affiliate

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

How to study Pollack's rule in 20 minutes

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

Frequently asked questions

What is Pollack's rule in simple terms?

Why does Pollack's rule 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 Pollack's rule?

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 Pollack's rule.