Exam Board:

1.1a: The CPU


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

Like many components of a computer, it is attached to the motherboard.

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

Computer Processor

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 structured is known as its architecture.

The most common type of computer architecture is Von Neumann.

Von Neumann Architecture

Von Neumann Architecture (1).png

This architecture is named after John von Neumann who developed the concept of a stored program computer in the 1940s. Before being able to store programs in memory, instructions had to be manually input by a human.

A computer with Von Neumann architecture stores both program instructions and data in the same memory (RAM).


Other architectures like Harvard have two separate memories - one for program instructions and another for data.

Data is transferred between components on pathways called buses.

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Questo's Questions

1.1a - The CPU:

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

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

2. Draw a diagram of the CPU, and label the four main components. [4]

3. Describe the purpose of:

  • a. The Control Unit [2]

  • b. The ALU [2]

  • c. The registers [2]

  • d. Cache memory [2]

4. Describe the key feature of Von Neumann architecture. [2]