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Year 8 · Autumn 1 · Computer Systems

Input, process, output, storage

TheoryPresent ▶

What this lesson covers

Topic 1 What a computer is

KS3 Computing · A computer takes information in, follows instructions to change it, gives a result out, and stores things for later. It does all of this with billions of tiny on/off switches.

Topic 8 Inside the computer

KS3 Computing · The CPU does the work, RAM holds what it's using now, and storage keeps everything long-term. The CPU repeats one loop: fetch, decode, execute.

Computer SystemsCambridge Lower Secondary Computing 0860

You will learn to

  • Identify the input, process, output and storage parts of a real device.
  • Sort twenty devices into input, output, processing and storage.
  • Explain why a computer uses switches with only two states: on and off.
  • Use the switch toy to show that one transistor stores one bit.

Success criteria

  • I can sort devices into input, process, output and storage, and give a reason for each.
  • I can follow one device, like a games console, through all four parts.
  • I can explain that a transistor is a switch, and one switch holds one bit.

Key words

Say each word, then read what it means. Every one is in the glossary too.

Input / output
Anything that gets information into the computer. Keyboard, mouse, touchscreen, microphone, camera, a temperature sensor.
Process
The computer follows instructions to change that information. Add two numbers. Move a character. Sort a list. The CPU does this.
Transistor
An electronic switch with no moving parts.
Hardware
The physical parts of a computer.
Software
Programs: instructions that tell hardware what to do.
Embedded system
A small computer built into a device for one job.
CPU
Central Processing Unit: the processor that runs instructions.
Register
Tiny storage inside the CPU, like the PC or ACC.
Bus
A set of wires that carries addresses, data or control signals between parts of the computer.
RAM
Random Access Memory: fast, volatile working memory.
Volatile
Loses its contents when the power goes off.
Cache
Small, very fast memory on the CPU chip.
Clock speed
How many cycles a CPU does per second, in GHz.

The explanation

Read it here, or open the study page below to go one step at a time with things to try.

Input, process, output

  1. Input: it receives information. You press a key, a microphone hears a sound.
  2. Process: it follows instructions to change that information. Add numbers, move a game character.
  3. Output: it gives a result back. Letters on a screen, sound from a speaker.
★Remember

Most computers also do storage: they keep information to use later.

e.g.Example

A washing machine is a computer too. Input: the dial. Process: choose a wash plan. Output: the drum turns.

A switch has two states

A light switch is either on or off. There is no half-on. A switch remembers one choice between two options. That is the whole trick of computing.

?Why?

Why only two states, not ten?

Electricity is never perfectly steady. Telling 'lots of power' from 'almost none' is easy. Telling level 6 from level 7 goes wrong when the signal wobbles.

Two states are also the simplest part to build, and they match yes/no and true/false perfectly.

Storage

TypeHow a bit is storedExamplesGoodBad
MagneticTiny magnetised areas on a spinning diskHard disk (HDD)Cheap, hugeMoving parts, slower
Solid stateCharge trapped in flash memorySSD, USB stick, phonesFast, silent, toughCosts more per GB
OpticalPits read by a laserCD, DVD, Blu-rayCheap to postSmall, slow, scratches
★Remember

Choose by: capacity, speed, portability, durability, reliability, cost.

Study it

Open the study page and go one step at a time.

Topic 1 · Year 7

What a computer is

A computer takes information in, follows instructions to change it, and gives a result out. It does all of this with billions of tiny on/off switches.

The steps for this lesson

Try it

Build it

Tinkercad · Starter

A switch and a light

Build a real circuit: press a button and a light comes on. Then let the Arduino press the switch for you, first with blocks, then in C++.

Check yourself

One question at a time. The reason shows after each answer.

Saved on this device.