Characteristics of the CPU (Cambridge International IGCSE Computer Science)

Spec point — 3.1.3 · "3 Understand what is meant by a core, cache and clock in a CPU and explain how they can affect the performance of a CPU"

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

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

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]