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Intermediate Topic 30 of 51 Computer Architecture & Logic

TLB

Cache of recent virtual-to-physical address translations.

How it works

The translation lookaside buffer is a small, fast cache inside the memory management unit that stores recent virtual-to-physical page translations. A hit gives the physical address in a cycle or two, whereas a miss triggers a page-table walk by hardware or the operating system. TLBs are usually fully or highly set-associative and tagged with address-space identifiers so that they need not be flushed on context switches.

Step-by-step walkthrough

  1. The CPU needs a virtual to physical translation.
  2. On a TLB hit the mapping returns in a cycle.
  3. On a miss the page table is walked.
  4. The mapping returns and is cached in the TLB.
  5. Locality makes hits common, so translation is almost free.

Where it is used

Every memory access on a modern CPU consults the TLB, so its hit rate strongly influences performance. Huge pages reduce TLB pressure for databases and virtual machines.

Common pitfall

A TLB miss adds latency, and workloads that touch many pages thrash it. After the operating system changes a mapping, the stale entry must be invalidated, including on other cores through TLB shootdowns, which are costly. Context switches without address-space IDs flush the TLB and hurt performance.

Where it fits in the course

TLB is topic 30 of 51 in Computer Architecture & Logic, rated Intermediate. It follows Virtual Memory in Hardware. The next topic is Instruction Pipelining.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Computer Architecture & Logic quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is TLB?
Cache of recent virtual-to-physical address translations. It belongs to Computer Architecture & Logic and is an intermediate-level topic.
Where do people use TLB?
Every memory access on a modern CPU consults the TLB, so its hit rate strongly influences performance.
What is the most common mistake with TLB?
A TLB miss adds latency, and workloads that touch many pages thrash it.
What should I learn before this topic?
Start with Virtual Memory in Hardware, the topic just before it in Computer Architecture & Logic.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Computer Architecture & Logic quiz.
Is TLB hard to learn?
It is an Intermediate topic. Be comfortable with the Beginner topics in this area first, then read the common pitfall carefully, since it is where most mistakes happen.
How long does it take to learn TLB?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to TLB?
Virtual Memory in Hardware, Instruction Pipelining, Cache Replacement Policies are closely connected. The full list is in the related topics section of this page.
What should I study after TLB?
Continue with Instruction Pipelining, the next topic in Computer Architecture & Logic.

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