Characteristics of the CPU (AQA GCSE Computer Science)

Revision Note

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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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