Factor 3: Cache Memory (L1, L2, L3)
Part of CPU Performance Factors — GCSE Computer Science
This key facts covers Factor 3: Cache Memory (L1, L2, L3) within CPU Performance Factors for GCSE Computer Science. Revise CPU Performance Factors in Systems Architecture for GCSE Computer Science with 15 exam-style questions and 12 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 5 of 7 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 5 of 7
Practice
15 questions
Recall
12 flashcards
Factor 3: Cache Memory (L1, L2, L3)
What It Is:
Cache is a small amount of very fast memory built directly into the CPU chip. It stores frequently-used data and instructions so the CPU doesn't have to wait for slower RAM.
Cache Levels:
- L1 Cache: Smallest (32-128 KB per core), fastest, located closest to CPU cores. Separate for instructions and data.
- L2 Cache: Medium (256 KB - 1 MB per core), slightly slower than L1, still very fast.
- L3 Cache: Largest (4-64 MB shared across all cores), slowest cache level but still much faster than RAM.
How It Works:
- When CPU needs data, it checks L1 first (fastest)
- If not in L1, checks L2
- If not in L2, checks L3
- If not in any cache, fetches from RAM (slowest) - called a "cache miss"
- Cache hit rate: % of time data is found in cache (higher is better)
How It Affects Performance:
- More cache = fewer RAM accesses = faster performance
- Cache is 50-100x faster than RAM!
- Example: L1 cache access = ~4 clock cycles, RAM access = ~200 clock cycles
- Larger cache means more data can be kept close to CPU