Computer Science • Data Representation

File Sizes

File Sizes — Learning objectives

Everything a computer stores is bits. Pick text, an image or a sound, see how it's stored, work out file sizes with the calculator, then test yourself with the challenges.

Explain how text, images and sound are represented in binary, and calculate the size of a file from how it's stored.

Where this fits

  • AQA: AQA A Level Computer Science (7517)
  • Cambridge: Cambridge IGCSE Computer Science (0478); Cambridge A Level Computer Science (9618); Cambridge AS Level Computer Science (9618); Cambridge A Level Information Technology (9626); Cambridge AS Level Information Technology (9626) Goes beyond Cambridge A Level Information Technology (9626): 9626 has why audio file size depends on sample rate and resolution; text and image file-size sums go beyond it. Goes beyond Cambridge AS Level Information Technology (9626): 9626 has why audio file size depends on sample rate and resolution; text and image file-size sums go beyond it.
  • IB: IB Computer Science HL; IB Computer Science SL
  • Pearson Edexcel International: Edexcel International GCSE Computer Science (4CP0); Edexcel International A Level Information Technology
  • USDP: USDP Computer Science

File Sizes — Key Terms

Key concepts in English, with te reo Māori, Chinese (Simplified) and Korean.

EnglishTe reo Māori中文（简体）한국어What it means on this page
Bitmoka位비트A single binary digit, 0 or 1.
Bytepaita字节바이트A group of 8 bits.
Characterno attested term字符문자A letter, digit, space, punctuation mark or control code such as a line break.
Character setno attested term字符集문자 집합The characters a computer can represent, each with its own number (code).
ASCIIno attested termASCII 码아스키(ASCII)A character set of 128 characters: 7 bits each, stored in one byte.
Unicodeno attested term统一码（Unicode）유니코드A character set for every writing system, stored in 1, 2 or 4 bytes per character (UTF-8, UTF-16, UTF-32).
Pixelpika像素픽셀(화소)The smallest dot of colour in an image.
Colour depthno attested term色深색 깊이The number of bits for each pixel; 2 to the power of it is the number of colours.
Image resolutionno attested term图像分辨率이미지 해상도The number of pixels across and down, e.g. 1920 × 1080.
Alpha channelno attested termAlpha 通道알파 채널Extra bits in each pixel that store how transparent it is.
Sampleno attested term采样值샘플(표본)One measurement of the height (amplitude) of a sound wave.
Sample rateno attested term采样率샘플링 레이트(표본화율)How many samples are taken each second, in hertz (Hz).
Sample resolution (bit depth)no attested term采样精度（位深度）샘플 해상도(비트 심도)The number of bits for each sample; it sets how many levels are possible.
Kibibyte (KiB)no attested termKiB（1024 字节）키비바이트(KiB)1024 bytes. A mebibyte (MiB) is 1024 KiB, a gibibyte (GiB) 1024 MiB. A kilobyte (kB) is 1000 bytes.
File sizeno attested term文件大小파일 크기How much storage a file needs, in bits or bytes.

On the te reo Māori column. Terms marked as gaps have no attested equivalent in the sources checked — Karaitiana Taiuru's Dictionary of Māori Computer and Social Media Terms, Paekupu, the Reserve Bank's te reo financial glossary, NZQA and Te Aka. No coinage is printed as though it were established; where a class needs one, commission it from Te Taura Whiri i te Reo Māori and credit the translator. Te reo Māori is not italicised and takes no plural "s".