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Data Storage and Compression

Data Representation · 4 question types

Practise

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 4% of your exam marks.

stable
Rare
Stable4%

File size calculations and lossless vs lossy compression are regular 3 to 4 mark questions.

These formulas were introduced in topic 2; they appear constantly in storage and compression questions too.

Sound file size

(bits) = sample rate (Hz) × sample resolution (bits) × duration (seconds)

A continuous sound waveform S(t) sampled at regular intervals T, with each blue dot a sample value Sᵢ
Source: Sampling a sound wave by Save My Exams

Image file size

file size (bits) = image width (pixels) × image height (pixels) × colour depth (bits per pixel)

Worked example

Calculating a sound file size

A music clip is recorded at a sample rate of 44 000 Hz with a sample resolution of 16 bits for a duration of 10 seconds.

Solution:

  • Total bits = sample rate × sample resolution × duration
  • Total bits = 44 000 × 16 × 10 = 7 040 000 bits
  • Convert to bytes: 7 040 000 ÷ 8 = 880 000 bytes
  • Convert to KiB: 880 000 ÷ 1024 = 859.375 KiB (≈ 859 KiB)