Characteristics of the CPU (AQA GCSE Computer Science)

Revision Note

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Robert Hampton

Written by: Robert Hampton

Reviewed by: James Woodhouse

Characteristics of the CPU

What are the common characteristics of the CPU?

  • There are 3 common characteristics 

    • Clock speed

    • Cache size

    • Number of processor cores

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

image-1---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 processor cores

  • A processor 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)

    • 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

cpu-cores-

Worked Example

1. State the purpose of the CPU

[1]

2. State what is meant by a dual-core 2.5Ghz processor

[2]

Answer

1. State the purpose of the CPU

  • The CPU performs the FDE cycle

  • Process instructions

[1]

2. State what is meant by a dual-core 2.5Ghz processor

  • Dual-core means there are two cores processing instructions

  • 2.5GHs means it can run 2.5 billion FDE cycles per second

[2]

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Robert Hampton

Author: Robert Hampton

Expertise: Computer Science Content Creator

Rob has over 16 years' experience teaching Computer Science and ICT at KS3 & GCSE levels. Rob has demonstrated strong leadership as Head of Department since 2012 and previously supported teacher development as a Specialist Leader of Education, empowering departments to excel in Computer Science. Beyond his tech expertise, Robert embraces the virtual world as an avid gamer, conquering digital battlefields when he's not coding.

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.