← Years 7–8 Digital Systems

CPU clock speed (GHz)

How many billions of cycles per second a CPU can run. A higher GHz usually means faster single tasks, but it is not the only measure of speed.

Part of: 7-8 Digital Technologies Vic Curric - Digital Systems and Security — Module 4, IGCSE Computer Science 0478 — 3.1 Computer Architecture — Module 25, ACARA Digital Technologies Years 7–8 — Hardware and Performance — Module 10

Understanding CPU clock speed (GHz) in Years 7–8 Digital Systems

What it does: With all else equal, more cycles per second means a single task is usually completed more quickly. The CPU with more cores can do more work at once, so the higher GHz number alone does not decide which is faster. Clock speed counts cycles per second. Storage is measured in bytes, such as GB, and is not what clock speed measures. GHz is only one measure of speed. Cores, RAM, storage type and the CPU design also affect performance. Look for the unit GHz. The storage line is measured in GB and tells you how much data fits on the drive.

Common mistakes: Clock speed is measured in gigahertz (GHz), not GB. GB (gigabytes) measures storage or memory. It should be 'Clock speed: 3.2 GHz'. One gigahertz is one BILLION cycles per second, not one million. It should be '1 GHz = 1 billion cycles/sec'.

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This module's key terms are also in a printable crossword (Modules 4–19) and word search (Modules 4–74).

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Learning
Duo
What does clock speed measure in a CPU?
How many cycles the CPU can run each secondHow much data the CPU can store
Matches
2.5 GHz = 2.5 thousand cycles per second
↓
GHz means billions of cycles per second, not thousands. 2.5 GHz is 2.5 billion cycles per second.
Applying
Meanings
Term
Clock speed (GHz)
Meaning
How many billions of cycles per second a CPU can run. A higher GHz usually means faster single tasks, but it is not the only measure of speed.
Practice
CPU clock speed: 3.6 GHz
Testing
Gaps
CPU: Ryzen 5, Clock speed: 3.6
Check Answer
Spots
1CPU: Core i5
2Clock speed: 3.2 GB

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Quick Questions

1. What does clock speed measure in a CPU?
A. How much data the CPU can store
B. How many cycles the CPU can run each second ✓
Clock speed counts cycles per second. Storage is measured in bytes, such as GB, and is not what clock speed measures.
2. A CPU is listed as 3.5 GHz. What does this mean?
A. It can run about 3.5 billion cycles per second ✓
B. It can run about 3.5 thousand cycles per second
Giga means billion, so 1 GHz is one billion cycles every second.
3. Which CPU will usually finish a single task faster, if everything else is similar?
A. A 4.2 GHz CPU ✓
B. A 2.1 GHz CPU
A higher GHz usually means the CPU completes more cycles each second, so single tasks are usually done faster.
4. True or false: GHz is the only thing that decides how fast a computer is.
A. False. Other things matter too, like the number of cores and the amount of RAM ✓
B. True. A higher GHz always makes the whole computer faster
GHz is only one measure of speed. Cores, RAM, storage type and the CPU design also affect performance.
5. Where would you find a CPU's clock speed when comparing laptops?
A. On the spec sheet, listed as a number followed by GB
B. On the spec sheet, listed as a number followed by GHz ✓
Clock speed is written in GHz. GB is used for storage and memory sizes.

Match the Pairs

3.6 GHz → The CPU can run 3.6 billion cycles every second
Clock speed: 4.5 GHz → A spec sheet line showing how fast the CPU can cycle
A higher GHz usually means a single task finishes faster → CPU A: 2.0 GHz | CPU B: 4.0 GHz -> B is usually faster
GHz is not the only measure of speed, because cores also matter → 3.0 GHz, 8 cores vs 3.5 GHz, 2 cores
2.5 GHz = 2.5 thousand cycles per second → GHz means billions of cycles per second, not thousands. 2.5 GHz is 2.5 billion cycles per second.
CPU X has the highest GHz, so it is always the fastest CPU → GHz is not the only measure of speed. Cores and other design features also affect speed, so a higher GHz is only usually faster.

Key Term

Clock speed (GHz)
How many billions of cycles per second a CPU can run. A higher GHz usually means faster single tasks, but it is not the only measure of speed.

Fill in the Blanks

1. CPU: Ryzen 5, Clock speed: 3.6 GHz
Hint: Type the unit written after the clock speed number on a spec sheet
2. 1 GHz = 1 billion cycles per second
Hint: Type the number word that tells how large one gigahertz is
3. Clock speed = cycles per second
Hint: Type what a CPU completes every second, as counted by clock speed
4. CPU A: 4.0 GHz CPU B: 2.5 GHz Faster single tasks: CPU A
Hint: Type the letter of the CPU with the higher clock speed
5. GHz is not the only measure of CPU speed
Hint: Type the word meaning GHz is not the sole measure of speed

Spot the Error

Question 1
A CPU: Core i5
B Clock speed: 3.2 GB
C RAM: 8 GB
Line B — Clock speed is measured in gigahertz (GHz), not GB. GB (gigabytes) measures storage or memory. It should be 'Clock speed: 3.2 GHz'.
Question 2
A 1 GHz = 1 million cycles/sec
B 3 GHz = 3 billion cycles/sec
C 4 GHz = 4 billion cycles/sec
Line A — One gigahertz is one BILLION cycles per second, not one million. It should be '1 GHz = 1 billion cycles/sec'.
Question 3
A OUTPUT "Compare clock speeds"
B IF 4.0 GHz < 2.0 GHz THEN
C OUTPUT "4.0 GHz is faster"
D ENDIF
Line B — 4.0 GHz is higher than 2.0 GHz, so the test must use >. With < the message about 4.0 GHz being faster would never be shown.
Question 4
A Laptop A: 2.4 GHz
B Laptop B: 3.6 GHz
C Higher GHz = more cycles/sec
D Faster clock: Laptop A
Line D — Laptop B has the higher GHz (3.6 vs 2.4), so it has the faster clock. Line 4 should say 'Faster clock: Laptop B'.
Question 5
A CPU X: 4.0 GHz, 2 cores
B CPU Y: 3.5 GHz, 8 cores
C GHz is the only measure
D Cores also affect speed
Line C — GHz is not the only measure of CPU speed. Other things, like the number of cores, matter too. It should say 'GHz is not the only measure'.

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