Units of information: a byte is a group of 8 bits.

The idea

A bit is a single binary digit, either 0 or 1, and it is the smallest unit of data a computer stores. A byte is a fixed group of 8 bits, so one byte can hold 2⁸ = 256 different bit patterns, numbered 0 to 255. This fixed size matters because hardware, memory addresses and character encodings are built around it: each ASCII character, for example, fits in one byte. To answer a multiple-choice question on this, count the bits carefully rather than assuming any small group is a byte. A nibble is 4 bits, so two nibbles make one byte. Remember that a byte is defined by its bit count, not by the value stored in it, so 00000000 and 11111111 are both valid bytes.

What earns the marks

• A bit is a single binary digit, 0 or 1, and is the smallest unit of data.
• A byte is defined as a group of exactly 8 bits.
• One byte gives 2⁸ = 256 distinct bit patterns, ranging from 0 to 255.
• A nibble is 4 bits, so two nibbles form one byte.
• The definition of a byte depends on its bit count, not on the value it stores.

Common mistakes and how to put them right

• Thinking a byte can be any small group of bits.

  Put it right by stating a byte is always exactly 8 bits.

• Confusing bits and bytes when counting.

  Put it right by remembering a bit is one digit and a byte is eight digits.

• Believing a byte must contain a meaningful value.

  Put it right by noting 00000000 is still a valid byte.

Exam tips

• Underline the word 'byte' or 'bit' in the question before choosing an answer.
• Recall the fixed figure of 8 bits whenever a byte is mentioned.
• Check each option against the exact definition rather than picking the first familiar-looking one.