Learn: Cache – Why the CPU Needs It

Welcome!Welcome back! You've already learned about the CPU, including its fetch-decode-execute cycle, registers, and components like the ALU and Control Unit. Today, we'll explore cache, a key part of the CPU that helps it work faster and more efficiently.

What is Cache?Cache is a small, fast type of memory located inside or very close to the CPU. It stores frequently used data and instructions to reduce the time taken to access them from RAM, which is slower. Cache helps the CPU run faster and boosts overall performance.

Why Does the CPU Need Cache?The CPU processes a huge number of instructions every second. Accessing RAM for every instruction would slow it down. Cache acts as a high-speed buffer between the CPU and RAM, storing data the CPU is likely to need repeatedly. This reduces waiting time and keeps the CPU working efficiently.

How Does Cache Work?When the CPU needs data, it first checks the cache. If the data is there, it uses it immediately (a cache hit). If not, it fetches the data from RAM (a cache miss). Cache is much faster than RAM, so using it speeds up processing significantly.

Levels of CacheCache is organised into levels: L1 (smallest and fastest, closest to the CPU), L2 (larger but slower), and sometimes L3 (shared across cores, larger and slower than L1 or L2). Each level balances size and speed to optimise performance.

Factors Affecting Cache PerformanceThe effectiveness of cache depends on its size (larger cache stores more data), speed (faster cache improves response time), and hit rate (percentage of requests successfully served from cache).

Review Time!Great work! You've learned about cache, its role in the CPU, how it works, and the factors that affect its performance. Now let's test your understanding with a few questions.