What is digital data?

Computers can only work with digital information. Everything that they process must first be turned into a digital signal in one of two states: 'on' or 'off'.

At a basic level a computer processor is a collection of switches which can either be on or off. These switches are known as transistors. The computer processes information by switching transistors on and off automatically.

Information from input devices must be digitised so the information can be processed.

Why do computers use binary?

In order to process information and store it, computers use binary code. Binary is a language composed of just the numbers 1 and 0.

It is stored in switches (transistors) as either on or off, just like a digital signal.

It can be stored on a computer disk using tiny areas magnetically charged with north and south - a bit like you find on a bar magnet. One direction stands for 1, and the other direction stands for 0.

When we say data is 'digitised' we mean it is turned into 1s and 0s for storage.

A large switch with the numbers 0 and 1.

How do you communicate using only on and off?

Using just on and off to send messages might seem very limiting. How can a computer process everything it does with just two signals?

Even in Victorian times, people used sequences of on and off to communicate. They sent messages through the electric telegraph and these messages had to be converted into Morse code.

Morse code is a series of dots and dashes that represent all the letters of the alphabet, numbers and punctuation.

The telegraph used a switch that was either on or off. The person listening at the far end of a telegraph wire could tell if the switch was on or off. By changing the length of time it was on, the person listening could tell if it was a 'dot' (a short signal) or a 'dash' (a longer signal).

So for example, ‘dot dash’ is the letter ‘a’.

Morse code allowed the transmission of coded messages though cables over great distance, just with a series of dots and dashes, or on and off signals.

Binary

Binary is just another code except that instead of dots and dashes you can use 0s and 1s to represent numbers and letters.

In binary, 01100001 could be the number 97, or it could represent the letter 'a'.

Morse code being tapped by hand.

What else can be turned into binary?

Everything that is stored on a computer is digitised. It has been turned into binary code to be processed and stored.

When you push keys on the keyboard you close the switch beneath the key. This information about which switch was closed is digitised, turned it into binary code and sent to the computer.

When an image is scanned into a computer it is converted into pixels. Each of these pixels is a small square of colour, with a binary number telling the computer what colour each square is. A scanner or camera is an input device that is designed to capture an image by digitising it.

A computer scanning an image of a girl
A scanner converts a picture into digital information that a computer can understand.

In this video Nate looks at how you can use a scanner to digitise photos so that you can easily share them with friends and family.

man about to flick a switch