Key Stage 3 computing · Computer systems

KS3 software, networks and how computer systems communicate

A computer system is more than hardware: software tells the hardware what to do, and systems must be able to talk to each other. In Years 7 to 9, children learn the main kinds of software, what an operating system does, and how data travels between devices and across networks in small pieces called packets.

Software and system communication, explained

Software is the set of programs that make hardware useful. It is usually divided into two groups. Application software does tasks for the user, such as a word processor, a game, a web browser or a photo editor. System software looks after the computer itself. The most important piece of system software is the operating system, which most children meet as the thing that makes a laptop or phone “start up”. Utilities, such as security and file-compression tools, are system software too.

The operating system does a great deal behind the screen. It manages memory, deciding which programs get how much RAM. It shares the CPU’s time between programs that seem to run at once. It manages files, storing them in folders on the drive. It controls hardware by using small programs called drivers, so that a program can print without knowing the details of one particular printer. And it provides the user interface, the icons, windows or touch controls. Software updates matter partly because they fix security weaknesses.

Programs themselves are usually written in a language people can read, but a processor only understands binary instructions. A translator converts one to the other. A compiler translates the whole program in one go, and an interpreter translates and runs it one line at a time. Some schools mention this at Key Stage 3, and it fits with the curriculum’s interest in how instructions are stored and run.

The curriculum also says pupils should understand how components “communicate with one another and with other systems”. Inside a computer, parts exchange data through connections on the motherboard. Between devices, communication happens over cables or wirelessly, for example with USB, Bluetooth or Wi-Fi. For systems to understand each other, they follow protocols, which are agreed sets of rules for how data is set out and sent. Many schools use computer networks to show this: a local area network (LAN) covers a small site such as a school, and a wide area network (WAN) joins sites across long distances. The internet is a very large collection of networks joined together.

Data does not travel across a network as a single block. It is split into small packets, each labelled with the address it is going to, the address it came from and its number in the sequence. Routers read these labels and pass each packet on towards its destination, and packets of the same message may take different routes. At the other end they are put back in order. This design allows many people to share the same links and lets traffic go around a fault. The exact level of detail depends on the school.

Words your child will hear

Operating system: System software that manages the hardware, memory, files and programs and provides the user interface.
Application software: Programs that let the user do a task, such as writing, browsing or playing a game.
Driver: A small program that lets the operating system control a particular piece of hardware.
Network: Computers and other devices joined together so that they can share data and resources.
Protocol: An agreed set of rules that lets devices understand each other when they communicate.
Packet: A small piece of a message, labelled with its destination and its position in the sequence.
Router: A device that passes packets between networks, for example between your home and the internet.

What the National Curriculum says

The programme of study for Key Stage 3 says:

Pupils should be taught to understand the hardware and software components that make up computer systems, and how they communicate with one another and with other systems
Aim: pupils can understand and apply the fundamental principles and concepts of computer science, including abstraction, logic, algorithms and data representation.

Objectives from the National Curriculum in England, © Crown copyright, used under the Open Government Licence v3.0.

Try it: following a web page request

Explain what happens, step by step, between typing a website address into a browser and the page appearing on the screen.

The browser is application software. It asks the operating system to send a request through the network hardware, which might be a Wi-Fi chip talking to the home router.
People type names, but computers need numbers. So before anything else, the device asks the Domain Name System (DNS), a kind of internet address book, to look up the website’s name and return its numerical address, called an IP address.
The request is sent as one or more packets. Each packet is labelled with the destination address, the sender’s address and a number showing its place in the sequence. The router passes the packets on, and routers along the way pass them closer to the destination.
The website’s computer, a server, runs software that receives the request and replies. The page is split into packets in the same way, and the packets can take different routes back.
Your device checks the packet numbers, puts them back in order and asks for any that are missing. The browser then uses the page data to display text and pictures on the screen. All these parties follow shared protocols, which is why a laptop and a server built by different people can understand each other.

The website’s name is looked up to find its IP address, the request travels as labelled packets passed on by routers to a server, the server replies with more packets, and the device reassembles them so the browser can show the page.

Common mistakes and how to help

Thinking the internet and the web are the same thing

People say “the internet” for everything they do online. The web, meaning pages viewed in a browser, is just one service running on the internet, alongside email and online games.

What helps: Describe the internet as the roads and the web as one kind of traffic on them. Ask which other things use the internet without using a browser.

Believing Wi-Fi is the internet

Devices show a Wi-Fi symbol when they are “online”, so the two seem to be the same thing. Wi-Fi only joins your device to the router wirelessly.

What helps: Ask what happens when the broadband line goes down but the router is still switched on: devices stay connected to the Wi-Fi network, but nothing outside the house can be reached.

Picturing a file travelling in one piece along one path

The easiest picture is a parcel posted from one house to another.

What helps: Use a puzzle picture: a message cut into numbered cards and sent by different routes, then put back in order. This explains why packets carry numbers.

Thinking the operating system is just what the screen looks like

Icons, menus and windows are all children see, so they assume that is the whole job.

What helps: Ask who decides which program can use the keyboard, where a saved file goes, or how a printer is recognised. The operating system manages all of these underneath.

How to help at home

Sort the software on a device. Look at a laptop or phone together and sort what is on it into application software and system software. Ask your child which one they would notice most if it stopped working. Updates are a good chance to explain why they matter.
Trace a message. When you send a message to a relative, ask your child to name every device and network it passes through, from your phone to the router or the mobile network, onwards and then out to the other person. Draw it as a map with arrows.
Play the packet game. Write a sentence on separate cards, number them on the back and shuffle them. A family member plays the receiver and puts them back in order using the numbers. Try removing one card and discuss how the receiver would notice.
Find the router and the cables. Find your home router and look at which devices connect by cable and which by wireless. Ask your child why the router needs a link to the outside world to reach a website. Look only; leave the settings unchanged.
Ask what each part is for. When something goes wrong, such as a printer that will not print, ask whether the problem is likely to be hardware, software, a driver or the network. Sorting a problem into categories like this is the same reasoning pupils use in lessons.

Leads on to

Key Stage 4: GCSE computer science