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GCSE Computer Science – Introduction
System Architecture
What is a Computer System?
  • A computer system is made up of hardware and software working together.
  • Hardware carries out the physical tasks.
  • Software provides the instructions.
  • A computer follows the cycle:
Input → Process → Store → Output
Example:
  • You type on a keyboard (input).
  • The CPU processes your typing.
  • The data may be stored.
  • The text appears on the monitor (output).


Key Computer Terms
Computer System
Definition:
A complete system consisting of hardware and software working together to process data.
Example:
A laptop contains hardware (keyboard, monitor, CPU) and software (Windows, apps).


Hardware
Definition:
The physical parts of a computer that you can see and touch.
Examples:
  • Keyboard
  • Mouse
  • Monitor
  • CPU
  • RAM
  • SSD
  • Hard Disk Drive (HDD)
  • Motherboard
Memory Tip:
Think of hardware as the body of the computer.


Software
Definition:
Programs and instructions that tell the hardware what to do.
Examples:
  • Windows
  • macOS
  • Google Chrome
  • Microsoft Word
  • Calculator app
Memory Tip:
Think of software as the computer’s instructions.


Input
Definition:
Data entered into a computer.
Examples:
  • Typing on a keyboard
  • Clicking a mouse
  • Speaking into a microphone
  • Scanning a barcode


Processing
Definition:
The CPU works on input data by following instructions.
Examples:
  • Performing calculations
  • Editing photos
  • Playing games
  • Opening applications


Storage
Definition:
Saving data so it can be used again later.
Examples:
  • Saving homework
  • Saving photos
  • Installing applications
Storage devices:
  • SSD
  • Hard Disk Drive (HDD)
  • USB Flash Drive


Output
Definition:
The result produced after processing.
Examples:
  • Text displayed on a monitor
  • Sound from speakers
  • Printed documents
  • Lights on a keyboard


CPU (Central Processing Unit)
Definition:
The CPU is the brain of the computer.
Main jobs:
  • Process data
  • Execute instructions
  • Control the operation of the computer
The CPU continually performs the:
Fetch → Decode → Execute Cycle


How Everything Works Together
Input
↓
CPU processes the data
↓
Data may be stored
↓
Output is produced


Real-Life Examples
Example 1 – Calculator App
Input:
  • Type 25 + 17
Processing:
  • The CPU performs the calculation.
Storage:
  • The result is temporarily stored in RAM.
Output:
  • The screen displays 42.


Example 2 – Writing Homework
Input:
  • Type an essay.
Processing:
  • The CPU converts keystrokes into letters.
Storage:
  • The document is saved to the SSD.
Output:
  • The completed essay appears on the monitor.


Example 3 – Watching YouTube
Input:
  • Click a video.
Processing:
  • The CPU and graphics processor decode the video.
Storage:
  • Part of the video is temporarily stored in RAM.
Output:
  • Video and sound are played.


Analogies
1. Restaurant
Input:
Customer places an order.
Processing:
Chef cooks the meal.
Storage:
Food waits in the kitchen or fridge.
Output:
Meal is served.


2. School Teacher
Input:
Student asks a question.
Processing:
Teacher thinks of the answer.
Storage:
Teacher remembers information.
Output:
Teacher gives the answer.


3. Washing Machine
Input:
Dirty clothes and wash programme selected.
Processing:
The controller runs the wash cycle.
Storage:
The selected settings are kept during the wash.
Output:
Clean clothes.


4. Coffee Machine
Input:
Press the coffee button.
Processing:
The machine prepares the drink.
Storage:
The recipe/settings are stored.
Output:
Coffee is dispensed.


5. Postal Service
Input:
A letter is posted.
Processing:
The sorting centre processes the mail.
Storage:
Letters wait in sorting offices if necessary.
Output:
The letter is delivered.


GCSE Exam Summary
Remember these five key points:
  • A computer system consists of hardware and software working together.
  • Hardware refers to the physical components you can touch.
  • Software consists of programs and instructions that tell the hardware what to do.
  • Every computer follows the cycle:
Input → Process → Store → Output
  • The CPU processes data, executes instructions and controls the operation of the computer.


Memory Tip
Think of a restaurant:
Customer orders
→ Chef cooks
→ Food waits in the kitchen
→ Meal is served
This is exactly the same as:
Input → Process → Store → Output
This version is organised like GCSE revision notes, making it easy to paste into OneNote, Word, Notion, or Google Docs while remaining concise and exam-friendly.

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