Understand that computers use binary to represent all data and instructions.

The idea

A computer's processor works with circuits that reliably hold one of two states, so everything it stores or acts on is encoded as patterns of 0s and 1s. Data such as a letter, a pixel colour or a sound sample is converted into a binary pattern, and instructions are also binary patterns that the processor decodes into operations such as add, load or jump. The same principle explains why a program and the data it processes can sit in the same memory: both are bit patterns, and the computer's interpretation depends on context. For example, the pattern 01000001 might be the integer 65 or the character A depending on whether it is being handled as a number or as text. Understanding this underpins number bases, character sets, images and sound.

What earns the marks

• Computers represent data using binary because hardware circuits have two stable states, commonly described as on and off or high and low voltage.
• All data types, including text, images, sound and integers, are stored as binary bit patterns.
• Instructions are also stored and processed as binary patterns, not as English words.
• The same bit pattern can be interpreted differently depending on the context in which it is used.
• Binary representation allows both data and instructions to be held in the same memory and processed by the same hardware.

Common mistakes and how to put them right

• Thinking computers store letters and pictures directly in their original form.

  Put it right by explaining that everything is converted to binary patterns first.

• Believing instructions are handled differently from data and are not binary.

  Put it right by stating that instructions are also binary patterns that the processor decodes.

• Assuming a bit pattern has one fixed meaning.

  Put it right by explaining that interpretation depends on context, such as number versus character.

Exam tips

• Link the answer to the two-state nature of computer circuits to justify why binary is used.
• Remember to mention instructions as well as data when asked what binary represents.
• Use a concrete example of one bit pattern being interpreted in two ways to show understanding.