What Affects CPU Performance?

The speed at which a CPU processes instructions depends on three key factors for OCR J277: clock speed, number of cores, and cache size. Understanding how each one affects performance — and their trade-offs — is essential exam knowledge.

1. Clock Speed

Clock speed is the number of fetch-decode-execute cycles the CPU can complete per second. It is measured in hertz (Hz) — typically gigahertz (GHz) for modern processors.

• 1 GHz = 1,000,000,000 (one billion) clock cycles per second
• A 3.5 GHz CPU performs 3.5 billion cycles every second
• Higher clock speed = more instructions processed per second = faster performance

However, increasing clock speed also increases heat output and power consumption. There is a physical limit to how fast a CPU can be clocked before it becomes unstable or requires impractical cooling.

2. Number of Cores

A core is an independent processing unit within the CPU. Each core can fetch, decode and execute instructions independently and simultaneously.

More cores allow true parallel processing — multiple tasks can be worked on at the same time. However, the software must be multi-threaded to take advantage of multiple cores. A single-threaded program will not run faster on a quad-core than a dual-core.

3. Cache Size

Cache is extremely fast memory located inside or very close to the CPU. It stores copies of frequently used instructions and data so the CPU can retrieve them much faster than fetching from RAM.

Cache Levels

When the CPU needs data, it checks L1 → L2 → L3 → RAM. The more data found in cache (cache hit), the faster the execution. A cache miss forces the CPU to wait for slower RAM. Larger cache = fewer cache misses = better performance.

Summary Table