Input devices

An input device is any piece of computer hardware used to provide data to a computer system. Examples include:

• keyboard
• mouse
• scanner
• digital camera
• webcam

Output devices

An output device is any piece of computer hardware used to communicate the results of data that has been processed.Examples include:

• monitor
• printer
• speaker
• headphones

Storage devices

A storage device is a piece of computer equipment which can be used to store data. Examples include:

• hard disk drive
• DVD drive
• USB stick

Hardware is the physical parts of the computer and software is the programs that run on a computer.

There is a close relationship between hardware and software. Without software, hardware is very limited and without hardware, software would not be able to run. They need each other.Software makes hardware useful. It gives it the instructions it needs to operate. When hardware runs software, it loads the software into its RAM.

There are two main types of software:

• systems software

• applications software

Systems software

Systems software helps run and maintain the computer. It includes the operating system, drivers and utility software.

Operating system

The biggest part of systems software is the operating system. It is an essential part that allows other systems software, and application software, to communicate with hardware.

All computers have an operating system. They cannot operate without one.

The operating system is needed to perform a number of tasks. It provides a user interface, manages the use of memory and the opening, closing, saving and deleting of files. Most operating systems have features that look after the security of the computer with usernames and passwords.

Examples of operating systems include Windows, Linux, Mac OSX, Android and iOS.

Applications software

Applications software is used to carry out tasks on a computer, such as writing an email, making a poster, doing homework and messaging friends. Some of the applications we might use to do this include a word processor, web browser and graphics software.

Some software, such as word processors, spreadsheets and desktop publishers are called general purpose software because it is possible to carry out lots of different tasks using that application.

Some software is called special purpose software because it performs one specific task. This might include a flight simulator, payroll software or an application for revising maths.

Applications are also used on smartphones to do lots of things, such as social networking, listening to music and messaging.

What is the purpose of the CPU?

The purpose of the CPU is to process data. The CPU is where processes such as calculating, sorting and searching take place. Whatever is done on our computers, such as checking emails, playing games and doing homework, the CPU has processed the data we use.

The CPU is made up of three main components, the control unit, the immediate access store and the arithmetic and logic unit.

The control unit

The control unit controls the flow of data within the system.

The control unit controls and monitors communications between the hardware attached to the computer. It controls the input and output of data, checks that signals have been delivered successfully, and makes sure that data goes to the correct place at the correct time.

Immediate access store

The immediate access store is where the CPU holds all the data and programs that it is currently using. You can think of it like the numbers typed into a calculator – they are being stored inside the calculator while it processes the calculations. The immediate access store is often referred to as the registers in the CPU.

Arithmetic and logic unit

The arithmetic and logic unit (ALU) is where the CPU performs the arithmetic and logic operations. Every task that your computer carries out is completed here. Even typing into a word processor involves adding binary digits to the file, and then calculating which pixels on the screen should change so that you can see the characters. The ALU’s operations fall into two parts:

the arithmetic part, which deals with calculations, eg 1 + 2 = 3

the logic part, which deals with any logical comparisons, eg 2>1

The Fetch-Execute Cycle

The basic operation of a computer is called the ‘fetch-execute’ cycle. The computer fetches the instruction from its memory and then executes it. This is done repeatedly from when the computer is booted up to when it is shut down.

Fetching the instruction

The first step the fetch-execute cycle carries out is fetching the instruction. The CPU fetches this from the main memory (the hard drive) and stores it in the CPU temporary memory, the immediate access store (the registers).

Once the instruction has been fetched, the CPU will need to understand the instruction to action it. This is called decoding.

Executing the instruction

When the instruction has been decoded, the CPU can carry out the action that is needed. This is called executing the instruction. The CPU is designed to understand a set of instructions - the instruction set

What is a network?

A network is two or more computers (or other electronic devices) that are connected together, usually by cables or Wi-Fi.

Some computer networks will have a server. A server is a powerful computer that often acts as a central hub for services in a network, eg emails, internet access and file storage. Each computer connected to a server is called a client.

A computer that is not connected to a network is called a standalone computer.

What are the benefits of a network?

Using a network allows you to share:

• hardware, such as a printer
• software, allowing multiple users to run the same programs on different computers
• data, so that other people can access shared work and you can access your data from any computer on the network

Types of network

There are two main types of network:

• a local area network (LAN)
• a wide area network (WAN)

Local area network (LAN)

A local area network is when computers or devices are connected together over a small geographical area, such as within a home, a building or one site. A LAN can be created to share data or hardware such as a printer, or to share an internet connection.

Wide area network (WAN)

A wide area network is when computers or devices are connected together over a large geographical area. For example, a company with an office in London and another in Beijing would use a WAN to allow the employees to share one network. Some companies will connect a number of LANs in different areas together to create a WAN. The biggest WAN we know is the internet.