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Units of Information

FoundationHigherAQA

Revise Units of Information for GCSE Computer Science with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA GCSE Computer Science (8525). Data is measured in bits and bytes, then kilobytes, megabytes, gigabytes and terabytes.

Free downloads

These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA specification. Every worksheet comes with a full mark scheme.

Foundation

WorksheetFoundation · PDFMark SchemeFoundation · PDF

Higher

WorksheetHigher · PDFMark SchemeHigher · PDF

Topic overview

Units of information measure how much data is stored, and they build up in a strict sequence.

A bit is a single binary digit. A nibble is 4 bits. A byte is 8 bits. From there each unit is 1000 times the last: a kilobyte is 1000 bytes, a megabyte is 1000 kilobytes, a gigabyte is 1000 megabytes, a terabyte is 1000 gigabytes, and a petabyte is 1000 terabytes.

The AQA specification uses 1000 rather than 1024, which is worth being firm about because older material often uses 1024. To convert upwards divide by 1000; to convert downwards multiply by 1000. Multiplying when you should divide gives an answer a million times out, which is usually obvious enough to catch.

Revision notes

The sequence

Bit: one binary digit. Nibble: 4 bits. Byte: 8 bits.

Kilobyte: 1000 bytes. Megabyte: 1000 kilobytes. Gigabyte: 1000 megabytes. Terabyte: 1000 gigabytes. Petabyte: 1000 terabytes.

Converting between units

To move up a unit, divide by 1000. To move down, multiply by 1000.

So 5000 kilobytes is 5000 ÷ 1000 = 5 megabytes. And 3 gigabytes is 3 × 1000 = 3000 megabytes. Bits to bytes uses 8, not 1000.

1000 versus 1024

The AQA specification uses 1000 for each step.

Older material often uses 1024, which is the exact power of two. Use 1000 in this course unless a question explicitly states otherwise.

Key points

  • A bit is one binary digit.
  • A nibble is 4 bits.
  • A byte is 8 bits.
  • Each larger unit is 1000 times the last.
  • Divide by 1000 to move up a unit.
  • Bits to bytes uses 8, not 1000.

Worked examples

Example 1

Convert 4000 megabytes to gigabytes. [2 marks]

Working

There are 1000 megabytes in a gigabyte, so divide by 1000identify the conversion
4000 ÷ 1000 = 4 gigabyteswork out the answer

Example 2

Convert 3 kilobytes to bits. [3 marks]

Working

3 kilobytes = 3 × 1000 = 3000 bytesconvert kilobytes to bytes
Each byte is 8 bits, so 3000 × 8convert bytes to bits
= 24 000 bitswork out the answer

Example 3

State how many bits are in a nibble and how many in a byte. [2 marks]

Working

A nibble is 4 bitsstate the nibble size
A byte is 8 bitsstate the byte size

Common mistakes

  • Using 1024 instead of 1000.

    The AQA specification uses 1000 for each step.

  • Using 1000 to convert bits to bytes.

    That conversion uses 8.

  • Multiplying when you should divide.

    Divide to move up a unit, multiply to move down.

  • Confusing a nibble with a byte.

    A nibble is 4 bits; a byte is 8.

Exam tips

  • Use 1000 between the larger units.
  • Use 8 between bits and bytes.
  • Divide upwards, multiply downwards.
  • Show each conversion step separately.

Key terms

Bit
A single binary digit.
Nibble
Four bits.
Byte
Eight bits.
Kilobyte
One thousand bytes.

Related topics

Written and reviewed against the current AQA specification. Spotted an error? Let us know.