AQA GCSE Computer Science 3.4 Computer systems: hardware and software, Boolean logic, the CPU, memory, storage and system software

What area 3.4 actually demands

Computer systems explains how a computer is built and how it runs programs. It is a definition-heavy area examined in Paper 2, where the marks reward precise wording and clear comparisons rather than calculation. You need to know the parts of a computer, the logic that underpins the processor, how the CPU runs instructions, the kinds of memory and storage, and the software that manages the whole machine.

This guide ties together the six dot-point pages for the area.

Hardware, software and logic

The area opens with the split between hardware (the physical parts you can touch, such as the CPU and keyboard) and software (the programs and data that run on it), which depend on each other. Boolean logic then introduces the AND, OR and NOT gates, their truth tables, and simple logic circuits, which are the building blocks of the processor.

The CPU and the fetch-execute cycle

The CPU processes instructions using its control unit, arithmetic logic unit and registers. It runs the fetch-execute cycle continuously: fetch the next instruction, decode it, then execute it. Performance is improved by a higher clock speed, more cores and more or larger cache.

Memory and storage

You must distinguish the kinds of memory: RAM (volatile main memory holding what is in use), ROM (non-volatile, holding start-up instructions), cache (fast memory near the CPU) and virtual memory (secondary storage used as extra RAM). Secondary storage is the non-volatile place data is kept permanently, in three types: magnetic (hard disk), optical (CD/DVD, read by laser) and solid state (flash memory, no moving parts).

System software

Finally, system software manages the machine. The operating system handles processor, memory, device, file, interface and security management, and utility software does maintenance tasks such as backup, compression, defragmentation and anti-malware.

Check your knowledge

A mix of recall and applied questions covering area 3.4. Attempt them, then check against the solutions.

1. State the difference between hardware and software. (2 marks)
2. State the output of an AND gate when its inputs are 1 and 0. (1 mark)
3. Name the three stages of the fetch-execute cycle. (3 marks)
4. Name the three main components of the CPU. (3 marks)
5. State one difference between RAM and ROM. (2 marks)
6. State the purpose of cache memory. (1 mark)
7. Name the three types of secondary storage. (3 marks)
8. Give two functions of an operating system. (2 marks)