Characteristics of the CPU (AQA GCSE Computer Science)

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

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