Year 8 · Autumn 1

Computer Systems · Lesson 1 of 5

Input, process, output, storage

TheoryTopic 1 What a computer isTopic 8 Inside the computer

Year 8 · Computer Systems · Lesson 1 of 5

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.

Year 8 · Computer Systems · Lesson 1 of 5

Success criteria

You have got it when you can say:

  • 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.

Year 8 · Computer Systems · Lesson 1 of 5

Retrieval starter

Questions from before. Write your answers, then show them.

  1. Last year

    Which shape is used for OUTPUT total?

    A RectangleB DiamondC Parallelogram

    C. Parallelogram

  2. Last year

    width × height × colour depth gives the size in…

    A KBB bitsC bytes

    B. bits

  3. Last year

    In a flowchart, a decision is a…

    A OvalB RectangleC Diamond

    C. Diamond

Year 8 · Computer Systems · Lesson 1 of 5

Key words (1 of 4)

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.

Year 8 · Computer Systems · Lesson 1 of 5

Key words (2 of 4)

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.

Year 8 · Computer Systems · Lesson 1 of 5

Key words (3 of 4)

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.

Year 8 · Computer Systems · Lesson 1 of 5

Key words (4 of 4)

Clock speed
How many cycles a CPU does per second, in GHz.

The explanation · step 1 of 3 · part 1 of 2

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.

The explanation · step 1 of 3 · part 2 of 2

Input, process, output (continued)

e.g.Example

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

The explanation · step 2 of 3

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.

The explanation · step 3 of 3

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.

Year 8 · Computer Systems · Lesson 1 of 5

Try it: Flip a switch

Year 8 · Computer Systems · Lesson 1 of 5

Quick quiz · 1 of 3

A microphone hearing your voice is…

  1. A Output
  2. B Input
  3. C Process

B. Input

Information is coming in to the computer.

Year 8 · Computer Systems · Lesson 1 of 5

Quick quiz · 2 of 3

Why do computers use 2 states instead of 10?

  1. A Ten states would be too cheap
  2. B Two is the biggest number
  3. C On and off are easy to tell apart reliably

C. On and off are easy to tell apart reliably

Wobbly signals make 10 levels easy to misread. On/off is reliable.

Year 8 · Computer Systems · Lesson 1 of 5

Quick quiz · 3 of 3

A game you download is…

  1. A Hardware
  2. B Software

B. Software

You can't touch it. It's instructions stored as 0s and 1s.

Year 8 · Computer Systems · Lesson 1 of 5

Exit ticket

Answer on paper before you go. Then check.

  1. What controls whether current flows through a transistor?

    A How hot it isB A tiny moving armC The voltage on its gate

    C. The voltage on its gate The gate is like a tap handle. Voltage on the gate opens the channel.

  2. Two transistors in a line (series) light a lamp only when…

    A Either gate is onB Neither gate is onC Both gates are on

    C. Both gates are on Current must pass through both, so both must be open. That is AND.