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GCSE Computer Science 03 — Data

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Topics include Bits, bytes and data units, Binary, denary and hexadecimal conversion, Binary arithmetic and shifts ( level), Character encoding: ASCII and Unicode, Images: pixels, resolution, colour depth and file size, Sound: sampling rate, bit depth and file size, Compression: lossless vs lossy, and Error checking: parity, checksums and basic validation.

ComputerScience EN
200 cards
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Bits, bytes and data units

All data is stored as bits; capacity and file sizes are measured in bytes and multiples.

Key points

  • 1 byte = 8 bits; common units: KB, MB, GB (and how they scale).
  • File size depends on what is stored (e.g., samples for sound, pixels for images).
  • Smaller files are faster to transmit and store.
  • Always show working when calculating storage requirements.

Worked example

Question

An image is 800×600 pixels with 24-bit colour. Estimate the uncompressed file size in bytes.

Solution

Pixels = 800×600 = 480,000.
Bits = 480,000 × 24 = 11,520,000 bits.
Bytes = 11,520,000 / 8 = 1,440,000 bytes (~1.44 MB if using 1 MB ≈ 1,000,000 bytes).

Common pitfalls

  • Mixing up bits and bytes (forgetting ÷8).
  • Forgetting to multiply by colour depth or number of samples.

Prerequisites

  • Multiplication/division
  • Understanding what a bit represents
Further resources