3.4 Computer systems

3.4.1 Hardware and software


Additional information

Define the terms hardware and software and understand the relationship between them.


3.4.2 Boolean logic


Additional information

Construct truth tables for the following logic gates:

  • NOT
  • AND
  • OR.

Students do not need to know about or use NAND, NOR and XOR logic gates.

Construct truth tables for simple logic circuits.

Interpret the results of simple truth tables.

Students should be able to construct truth tables which contain up to three inputs.

Create, modify and interpret simple logic circuit diagrams.

Students should be able to construct simple logic circuit diagrams which contain up to three inputs.

Students will only need to use AND, OR and NOT gates within logic circuits.

Students will be expected to understand and use the following logic circuit symbols:

3.4.3 Software classification


Additional information

Explain what is meant by:

  • system software
  • application software.

Give examples of both types of software.


Understand the need for, and functions of, operating systems (OS) and utility programs.

Understand that the OS handles management of the:

  • processor(s)
  • memory
  • I/O devices
  • applications
  • security.

3.4.4 Systems architecture


Additional information

Explain the Von Neumann architecture.


Explain the role and operation of main memory and the following major components of a central processing unit (CPU):

  • arithmetic logic unit
  • control unit
  • clock
  • bus.

A bus is a collection of wires through which data is transmitted from one component to another. Main memory will be considered to be any form of memory that is directly accessible by the CPU, except for cache and registers.

Explain the effect of the following on the performance of the CPU:

  • clock speed
  • number of processor cores
  • cache size
  • cache type.

Understand and explain the Fetch-Execute cycle.

The CPU continuously reads instructions stored in main memory and executes them as required:

  • fetch: the next instruction is fetched to the CPU from main memory
  • decode: the instruction is decoded to work out what it is
  • execute: the instruction is executed (carried out). This may include reading/writing from/to main memory.

Understand the differences between main memory and secondary storage.

Understand the differences between RAM and ROM.

Students should be able to explain the terms volatile and non-volatile.

Secondary storage is considered to be any non-volatile storage mechanism not directly accessible by the CPU.

Understand why secondary storage is required.


Be aware of different types of secondary storage (solid state, optical and magnetic).

Explain the operation of solid state, optical and magnetic storage.

Discuss the advantages and disadvantages of solid state, optical and magnetic storage.

Students should be aware that SSDs use electrical circuits to persistently store data but will not need to know the precise details such as use of NAND gates.

Explain the term 'cloud storage'.

Students should understand that cloud storage uses magnetic and increasingly solid state storage at a remote location.

Explain the advantages and disadvantages of cloud storage when compared to local storage.


Understand the term 'embedded system' and explain how an embedded system differs from a non-embedded system.

Students must be able to give examples of embedded and non-embedded systems.