Exam Board:

1.1a: The CPU


The Central Processing Unit (CPU) is the most important component in any computer system.

The purpose of the CPU is to process data and instructions by constantly repeating the fetch - execute cycle.

CPU Components

The Control Unit (CU) sends control signals to direct the operation of the CPU


Control signals and timing signals are sent to the ALU and other components such as RAM.

It also decodes instructions as part of the F-E cycle.

ALU stands for ‘Arithmetic and Logic Unit’.


It performs simple calculations and logical operations.

CPU Diagram (with Cache) (1).png

A register is a temporary storage space for one instruction or address.

Different registers are used during the FE cycle.

Cache memory is used to temporarily store data that is frequently accessed.

Cache memory is split into different levels. 


Cache is slower to access than the registers but much faster than RAM.

Computer Architecture

The way a computer is designed and laid out is known as its architecture.

The most common type of computer architecture is Von Neumann.

Von Neumann Architecture

Von Neumann Architecture (1).png

The CPU is the most important component in Von Neumann architecture as it is constantly fetching and decoding instructions from RAM and controlling the other parts of the system.

Von Neumann architecture also stores both program instructions and data in memoryBeing able to store programs in memory allows computers to be re-programmed for other tasks - this enables it to multitask and run several applications at the same time. 

Data input and output is another key feature of this architecture.

Questo's Questions

1.1a - The CPU:

1a. What does 'CPU' stand for? [1]

1b. What is the purpose of the CPU? [2]

2a. Draw a diagram of the CPU, use the same symbols as shown on this page. [4]

2b. Label the four main components of the CPU. [4]

3. Describe the purpose of:

  • a. The Control Unit [2]

  • b. The ALU [2]

  • c. The registers [2]

  • d. Cache memory [2]

4a. Describe the key features of Von Neumann architecture. [3]

4b. Explain why storing data in memory is important. [1]