Factors affecting CPU performance

Overview

Clock speed and a worked GHz figure, overclocking, how cache size and the number of cores affect performance, and why more cores or a faster clock do not always help.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What is clock speed?

   Model answer

   Clock speed is the number of clock cycles the CPU completes each second. A higher clock speed means more instructions can be fetched and executed per second.

2. 2

   State the unit used to measure clock speed.

   Model answer

   Clock speed is measured in hertz (Hz), meaning cycles per second. A modern CPU is usually rated in gigahertz (GHz).

3. 3

   A CPU has a clock speed of 3.2 GHz. How many clock cycles does it complete each second?

   Model answer

   The CPU completes 3,200,000,000 clock cycles each second. One gigahertz is 1,000,000,000 hertz, so 3.2 × 1,000,000,000 = 3,200,000,000.

4. 4

   Why does a higher clock speed usually improve performance?

   Model answer

   A faster clock lets the CPU fetch, decode and execute more instructions every second. Programs therefore complete their tasks in less time.

5. 5

   Why can manufacturers not keep increasing clock speed?

   Model answer

   A faster clock makes the CPU use more power and produce more heat. Too much heat makes the CPU unstable and can damage it, so cooling sets a practical limit.

6. 6

   What is overclocking?

   Model answer

   Overclocking is running a CPU at a higher clock speed than its manufacturer set. The extra heat can cause crashes or shorten the life of the processor.

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