System Performance (Cambridge (CIE) A Level Computer Science) : Revision Note

Cores

What is a core?

• A core acts like a mini CPU, it can fetch, decode, and execute instructions on its own

• Each core has its own:

  • Control Unit (CU)

  • Arithmetic Logic Unit (ALU)

  • Registers

• A CPU with more than one core is a multicore CPU

• Allows for parallel processing, multiple instructions are processed at the same time

• Example:

  • A dual-core processor has 2 cores

  • A quad-core processor has 4 cores

• More cores = better performance, especially for powerful programs

  Example:

  • A quad-core CPU running at 3GHz

  • 4 cores × 3 billion = 12 billion instructions per second

• A dual-core processor isn't always twice as fast as a single-core

  • Some time is used for organising tasks between cores

• Not all tasks can be split across cores

  • Some tasks are sequential and must be done step-by-step

Clock speed

What is clock speed?

• The clock controls the timing of operations inside the CPU

• It constantly switches between 0 and 1, each switch is called a state change

• A state change can represent one step in the fetch-decode-execute cycle

  • Some instructions may take more than one cycle

• Clock speed measures how many state changes happen per second

• 1 cycle per second = 1 Hz

• A typical clock speed is around 2.3 GHz

  • That’s 2.3 billion cycles per second

• A higher clock speed means the CPU can execute more instructions per second

• This helps the computer run tasks more quickly and efficiently

Cache memory

What is cache memory?

• Cache is part of primary storage

• Stores frequently used data and instructions

• Located closer to the CPU than RAM, so it’s faster to access

• Some cache is built directly into each processor core

• Speeds up the performance of the CPU

• More cache = more data stored nearby = less time waiting for data from RAM

• Example:

  • A website you visit often can be stored in the cache

  • Next time you visit, it loads faster

  • If the website updates, the cached version is updated too

Levels of cache

Bus width

What is bus width?

• Bus width is the number of bits a bus can carry at once

• A wider bus can transfer more bits in a single operation

• Example:

  • A 32-bit bus transfers 32 bits at a time

  • A 64-bit bus transfers 64 bits at a time

• Increases performance, more data can be moved in the same amount of time

• A wider data bus means:

  • Faster processing

  • More efficient memory access

• Important for high-performance tasks like gaming, video editing, or large data processing