This key facts covers Factor 1: Clock Speed (Measured in GHz) within CPU Performance for GCSE Computer Science. Revise CPU Performance in 3.4 Computer Systems for GCSE Computer Science with 15 exam-style questions and 12 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 3 of 8 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Factor 1: Clock Speed (Measured in GHz)
What It Is:
The CPU operates on a "clock" that ticks at a regular rate. Clock speed measures how many times per second the clock ticks. Each tick is called a cycle.
Measured In:
- Hertz (Hz): 1 cycle per second
- Megahertz (MHz): 1 million cycles per second (1,000,000 Hz)
- Gigahertz (GHz): 1 billion cycles per second (1,000,000,000 Hz)
- Example: A 3.2 GHz CPU ticks 3.2 billion times every second!
How It Affects Performance:
- Higher clock speed = more instructions per second
- The CPU can complete more FDE cycles in the same time
- Example: 4 GHz CPU is roughly twice as fast as 2 GHz CPU (same architecture)
- BUT: Higher speed = more heat and power consumption
Important Limitation:
Not all instructions take the same number of cycles! A simple ADD might take 1 cycle, but a MULTIPLY might take 3-4 cycles. A DIVIDE could take 10+ cycles. So doubling clock speed doesn't always double real-world performance.
Practice questions for CPU Performance
What does clock speed measure in a CPU?
Describe three factors that affect CPU performance.