Think about making fresh juice. You put fruit and water into the blender, the blender whizzes it all up, juice pours out into your glass, and what is left goes into the fridge for later. A computer works in almost the same way! Something goes in, something happens to it, something comes out, and some of it is kept for later.
In this post:
- The four main jobs of a computer system: input, processing, output and storage
- The devices that do each job
- What happens if one part is missing
- Activities and a short quiz
Input → Processing → Output (and Storage)
data goes in
keyboard, mouse, microphone
the CPU works on it
processor + memory
results come out
screen, printer, speakers
kept for later
hard disk, SSD, USB drive, cloud
- Input is how data gets into the computer. Input devices include the keyboard, mouse, touchscreen, microphone, webcam, scanner, barcode reader and game controller.
- Processing is when the computer works on the data: calculating, sorting, comparing, following the instructions in a program. This is done by the CPU (Central Processing Unit, or processor), often called the brain of the computer. The CPU uses main memory (RAM) to hold whatever it is working on right now.
- Output is how the results come out so that we can see, hear or use them. Output devices include the monitor, printer, speakers, headphones and projector.
- Storage keeps data and programs for later, even when the power is off. Storage devices include hard disk drives, solid state drives (SSDs), USB flash drives, memory cards and cloud storage on the Internet.
Notice the arrows: data flows from input to processing to output. Storage arrows go both ways because the processor saves data to storage and also loads it back.
Image source: File:Personal computer, exploded 5.svg (Wikimedia Commons)
What if one part is missing?
| If there is no… | What happens? |
|---|---|
| Input | You cannot give the computer any data or instructions, so it has nothing to work on. |
| Processing | Nothing happens to the data at all. There are no answers and no results. |
| Output | The computer may do the work, but you cannot see or hear the results. |
| Storage | Everything is lost when you switch off, including your work and even the programs. |
Watch: what makes a computer a computer?
This video from Code.org explains the four things that every computer does. Listen for the words input, storage, processing and output.
Video: How Computers Work: What Makes a Computer, a Computer? – Code.org – https://www.youtube.com/watch?v=mCq8-xTH7jA
Activity: input, processing, output or storage?
Try it: sort the devices
Drag each device into the job it does. On a phone or tablet, tap a device and then tap the box. Then click “Check my sorting”.
Input
Processing
Output
Storage
Activity: follow the data
Try it: which stage is it?
Here are the steps of two everyday jobs. Choose the stage for each step.
| You put your card in the ATM and type your PIN | |
| The bank’s computer checks your PIN and your balance | |
| The cash comes out and a receipt is printed | |
| Your new balance is saved in the bank’s records | |
| You tap a song title on your phone | |
| The phone works out which file to play | |
| The song plays through your earphones | |
| The song was downloaded and kept on your phone last week |
Drawing task
Draw a typical computer system (computer, monitor, keyboard, mouse, printer and speakers). Label each part and write I, P, O or S beside it. Add arrows to show which way the data flows.
Self-check quiz
Click the best answer. You get feedback straight away; only your first click counts towards your score.
1. Which part of the computer does the processing?
2. Which of these is an output device?
3. Why do we need storage?
4. Typing your name on a keyboard is an example of…
5. What would happen if a computer had no output devices?
6. Why does the storage arrow point both ways?
Related posts on islandclass.org
- The Functions of the Main Components of a Computer System
- Data and Information
- What is hardware?
- Peripheral Device
- Videos: The Major components of a computer system
- The Main Components of a Computer System (Live Class 1P) – 2025-10-23_11-15-38 – recording of our Form 1 class
For later, in Forms 4–5 (CSEC IT): these go deeper and are for when you reach CSEC Information Technology.
- Inside the Computer: Input, Processing, Memory, Storage and Output (IPOS)
- Choosing the Right Input and Output Devices
Next: Why Computers Are So Useful
Syllabus link: Forms 1–3 ICT curriculum, Module 2, Objective 2.2 – explain the functions of the main components of a basic computer system.
Attributions to media used in this post:
- Personal computer, exploded 5.svg – Gustavb – CC BY 2.5 (via Wikimedia Commons)
- Video: How Computers Work: What Makes a Computer, a Computer? – Code.org (YouTube)
Updates
2026/10/21
– Fixed the activity code so its buttons keep working.
© 2026 Vedesh Kungebeharry. All rights reserved.