1.2: CPU Performance
Exam Board:
Cambridge OCR
Specification:
GCSE - J277
Watch on YouTube:
CPU Performance
How these CPU characteristics affect the performance of a computer system:
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Clock speed
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Cache size
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Number of cores
What You Need to Know
Clock Speed
A computer has a component called a clock, which produces regular electrical pulses. Clock speed is the number of clock pulses the CPU receives per second.
It is measured in gigahertz (GHz). For example, 3.5 GHz is 3.5 billion pulses per second.
The Control Unit (CU) uses each clock pulse to send control signals that coordinate operations within the computer.
A higher clock speed improves the performance of the CPU because more fetch-execute cycles can be completed per second.
This means more instructions can be executed in the same amount of time, so tasks can be completed faster.
Cache Size
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Cache memory is fast, temporary storage inside (or very close to) the CPU, which stores frequently accessed data and instructions.
It is typically split into three levels (L1, L2 and L3), with each level generally being larger but slower than the previous level.
As data and instructions are fetched during the fetch-execute cycle, frequently accessed data and instructions can be stored in cache, reducing the need to repeatedly fetch them from RAM, which is slower to access.
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A CPU with a larger cache can store more frequently accessed data and instructions, improving performance because they can be accessed faster from cache than from RAM.
Number of Cores
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Some CPUs have multiple cores. A core is an individual processing unit within the CPU, containing components such as a control unit, ALU, registers and cache.
Each core can independently perform the fetch-execute cycle.
A CPU with more cores can have higher performance because it can process more instructions at the same time.
However, performance may not improve if one core must wait for another to complete its task. Also, some software is not designed to use multiple cores, so it will not benefit from having additional cores.
Single-core
Dual-core
Quad-core
Octa-core
Questo's Questions
1.2 - CPU Performance:
Clock Speed
1a. What is clock speed? What is it measured in? [2]
1b. Explain how a higher clock speed improves performance. [2]
Cache Size
2a. What is cache memory? [2]
2b. Describe why a larger cache size may mean performance is higher. [4]
Number of Cores
3a. What is a core? [2]
3b. Explain why a quad-core processor should have a higher performance than a dual-core processor. [3]
3c. Explain two reasons why having more cores doesn't necessarily mean the performance will be better. [2]