2.1.2 The CPU

The Central Processing Unit (CPU)

(a) state the purpose of the CPU

The CPU is the core of every computer system, containing the control unit, the ALU (arithmetic and logic unit) and cache memory. The control unit works with the CPU to control flow of data within the system. The ALU carries out all of the arithmetic and logical operations within the CPU.

(b) describe the function of the CPU as fetching and executing instructions stored in memory

The CPU has access to the main memory (RAM-Random Access Memory) which stores data, applications and the operating system while the computer is in use, but loses data when powered off. Cache memory is the high speed memory storing data waiting to be processed.

When a computer is switched on, the CPU runs a fetch-execute cycle, which fetches instructions from the ROM-read only memory (A store for data in a computer that cannot be overwritten and not lost when powered off). The CPU then executes the program commands to get the OS started.

(c) explain how common characteristics of CPUs such as clock speed, cache size and number of cores affect their performance

• Dual core/quad core processor- A CPU with 2/4 processors which can fetch, decode and execute at the same time as one another, so more instructions can be processed.
• More cache memory- reduces time taken to access data which is more efficient.
• Faster clock speed- a faster clock speed allows for more calculations per second.