Skip to content
Get started
ICT 04171.1

Hardware, software and main components

The difference between hardware and software, and what the CPU, RAM and ROM do.

Learning objectives

What you need to be able to do

Teacher-mapped phrasing — check against the official Cambridge syllabus for exact wording.

  • 1.1.1Define hardware and software and identify the main components of a computer system.
  • 1.1.2Describe the difference between RAM and ROM and the role of the CPU.

5 minute read

Hardware, software and main components

Hardware and software

Hardware is the physical components of a computer system — things you can touch, such as the keyboard, monitor and hard disk. Software is the programs that control the computer and tell the hardware what to do. It has no physical form. Software splits into two kinds:

  • System software — runs the computer itself: the operating system, device drivers, utilities and compilers.
  • Application software — lets the user do a task: word processors, spreadsheets, browsers, games.

The main internal components

  • CPU (central processing unit) — processes data and executes instructions. Often called the "brain", it fetches, decodes and executes each instruction in turn.
  • RAM (random access memory) — holds the data and programs currently in use. It is volatile: switch the power off and the contents are lost. RAM can be read from and written to.
  • ROM (read only memory) — holds the start-up instructions (the bootstrap/BIOS). It is non-volatile: contents survive power loss. As the name says, it is normally only read from.

Input, process, output, storage

Every system follows the same model: data is input, the CPU processes it, results are output, and data is kept in storage for later. Recognising which stage a device belongs to answers a lot of exam questions on its own.

Think of it like this

RAM is your desk and ROM is the instruction card screwed to the wall. You spread out whatever you are working on across the desk, and clearing the desk at the end of the day loses it — but the card on the wall is still there tomorrow to tell you how to start.

Worked examples

Method, step by step

A computer loses all unsaved work when the power fails, but still starts up normally afterwards. Explain this using RAM and ROM.

  1. 1Unsaved work is held in RAM while it is being used.
  2. 2RAM is volatile, so its contents are lost when power is removed — hence the lost work.
  3. 3The start-up instructions are held in ROM, which is non-volatile, so they survive and the machine can boot.

The unsaved work was in volatile RAM, which loses its contents without power. The start-up instructions are in non-volatile ROM, which retains them, so the computer still boots.

Common misconceptions

  • Calling RAM "memory" and the hard disk "storage" as if only one holds data. Both store data; the difference is volatility and speed.
  • Thinking more RAM makes the CPU faster. More RAM lets more programs run at once without slowing down, but does not increase processing speed itself.
  • Believing ROM and a hard disk are the same because both are non-volatile. ROM holds the fixed start-up instructions; the hard disk holds the user's files and installed programs.

In the exam

  • When comparing RAM and ROM, give three contrasts: volatile vs non-volatile, read/write vs read-only, and what each holds (current work vs start-up instructions).
  • If asked to classify software, say whether it is system or application software **and** give the reason — "it controls the hardware" or "it performs a task for the user".