Timing Technology — Clocks, Crystals & Signals
What makes a computer tick — literally?
- Explain what a clock signal is and why digital circuits need one
- Describe the role of a crystal oscillator
- Convert clock speed (e.g. GHz) to cycles per second
Overview
Every digital device has a heartbeat. That heartbeat is the clock signal — a steady square wave generated by a tiny quartz crystal — that keeps every part of the CPU in step.
What is a clock signal?
A clock signal is a regular square wave that alternates 0 and 1. On each 'tick', all the transistors in a CPU move to their next state together. Without it, calculations would fall out of step.
Crystal oscillators
A quartz crystal vibrates at a very precise frequency when voltage is applied. That vibration is amplified into the clock signal. Cheap watches, phones and CPUs all rely on the same trick.
Clock speed maths
1 Hz = 1 cycle per second. 1 GHz = 1,000,000,000 cycles per second. A 3.2 GHz CPU does 3.2 billion clock ticks per second — but not necessarily 3.2 billion instructions, because some instructions take several ticks.
Clock-speed comparison
- Compare 3 CPU spec sheets: e.g. 2.4 GHz, 3.2 GHz, 4.0 GHz.
- Convert each to cycles per second.
- Discuss: is the fastest clock always the fastest CPU? Why not?
- What is a clock signal?
Reveal answer
A regular square wave that keeps every part of a digital circuit in step.
- 3.2 GHz equals how many cycles per second?
Reveal answer
3,200,000,000 (3.2 billion) cycles per second.
- Is a 4.0 GHz CPU always faster than a 3.2 GHz CPU?
Reveal answer
Not necessarily — cores, cache and architecture also matter.
Find the clock speed of your phone's processor. What generation is it?