GCSE > Computer Science > AQA > GCSE Computer Science > COMPUTER SYSTEMS: Memory and storage > Units of data storage
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COMPUTER SYSTEMS: Encoding and compression

COMPUTER SYSTEMS: Network topologies

COMPUTER SYSTEMS: Wired and wireless networks, protocols, and layers

COMPUTER SYSTEMS: Threats to computer systems and networks

COMPUTER SYSTEMS: Operating systems and utility software

COMPUTER SYSTEMS: Impact of technology on society

ALGORITHMS AND PROGRAMMING: Types of data

ALGORITHMS AND PROGRAMMING: Producing robust programs

ALGORITHMS AND PROGRAMMING: Designing, creating, and refining algorithms

ALGORITHMS AND PROGRAMMING: Programming languages

ALGORITHMS AND PROGRAMMING: Artificial Intelligence (AI)

  • All data in a computer (text, images, sound, etc.) must be stored in binary (0s and 1s). Computers only understand on (1) and off (0) signals using electronic circuits.
  • Increments of storage space go up in a geometric sequence (same multiplier), in this case ×2 (i.e. 1, 2, 4, 8, 16, 32…).
  • File size calculations: to determine how much storage a file will need: 
    • Text file size = bits per character × number of characters. There are usually 8 bits (1 byte) per character (ASCII). 
    • Image file size = colour depth × image width × image height. This is measured in bits. Colour depth = bits per pixel. 
    • Sound file size = sample rate × bit depth × duration (seconds), often multiplied by the number of channels (e.g. 2 for stereo).
  Size
Unit Decimal Binary
Bit Smallest unit (0 or 1)
Nibble 4 bits
Byte 8 bits
Kilobyte 1,000 bytes 1,024 bytes
Megabyte 1,000 KB 1,024 KB
Gigabyte 1,000 MB 1,024 MB
Terabyte 1,000 GB 1,024 GB
Petabyte 1,000 1,024 TB

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