Characteristics of the CPU (Cambridge (CIE) IGCSE Computer Science)

Revision Note

James Woodhouse

Written by: James Woodhouse

Reviewed by: Lucy Kirkham

Characteristics of the CPU

What are the common characteristics of the CPU?

  • There are 3 common characteristics 

    • Clock Speed

    • Cache Size

    • Number of Cores

  • Each of these characteristics has a significant impact on the performance of the CPU

Image of the CPU


How do the characteristics of the CPU affect performance?

Clock speed

  • The clock speed is measured in Hertz (Hz)

  • The clock speed measures the number of fetch-decode-execute cycles that can take place in 1 second

  • The faster the clock speed, the more instructions can be fetched and executed per second

  • Modern computers have a clock speed in Gigahertz (GHz), meaning billion

  • A clock speed of 3.5GHz can perform up to 3.5 billion instructions per second

 Cache size

  • Cache is very small, very fast memory on or close to the CPU 

  • Cache is used as temporary storage to provide quick access to a copy of frequently used instructions and data

  • The larger the cache size, the more frequently used instructions or data can be stored

  • This results in the CPU having to complete fewer fetch cycles from memory (RAM), speeding up the performance

  • Cache also has a significantly faster read/write speed than RAM, making it much quicker to retrieve instructions from there instead of from memory (RAM) 

Number of cores

  • A core works like it is its own CPU

  • Multiple core processors mean they have multiple separate processing units that can fetch, decode and execute instructions at the same time

  • For example, a dual-core processor would have 2 processing units, each with their own

    • Control Unit (CU)

    • Arithmetic Logic Unit (ALU)

    • Accumulator (ACC)

    • Registers 

  • Multi-core processors can run more powerful programs with greater ease

  • Multiple cores increase the performance of the CPU by working with the clock speed

    • Example: A quad-core CPU (4 cores), running at a clock speed of 3Ghz

      • 4 cores x 3GHz

      • 4 x 3 billion instructions

      • 12 billion instructions per second

Image of multiple cores

Worked Example

One computer has a single core processor and the other has a dual core processor.

Explain why having a dual core processor might improve the performance of the computer

[2]

Answer

Any 2 from:

  • The computer with the dual core processor has two cores/double the amount of cores [1]

  • Parallel processing can take place [1]

  • Each core can execute a separate instruction at the same time [1]

  • Each core can process instructions independently of each other [1]

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James Woodhouse

Author: James Woodhouse

Expertise: Computer Science

James graduated from the University of Sunderland with a degree in ICT and Computing education. He has over 14 years of experience both teaching and leading in Computer Science, specialising in teaching GCSE and A-level. James has held various leadership roles, including Head of Computer Science and coordinator positions for Key Stage 3 and Key Stage 4. James has a keen interest in networking security and technologies aimed at preventing security breaches.

Lucy Kirkham

Author: Lucy Kirkham

Expertise: Head of STEM

Lucy has been a passionate Maths teacher for over 12 years, teaching maths across the UK and abroad helping to engage, interest and develop confidence in the subject at all levels.Working as a Head of Department and then Director of Maths, Lucy has advised schools and academy trusts in both Scotland and the East Midlands, where her role was to support and coach teachers to improve Maths teaching for all.