Fiducia TogetherCompression
Making a file smaller. Lossy throws information away; lossless does not.
Please note: This page explains a word or a process in education. It is general information about the system, the law and the guidance in England — not advice about your child, your school or your exam. If a decision is going against you, get advice from one of the free services we link to before you agree to anything or miss a deadline. If you are revising, check your own exam board's specification: boards word things differently and yours is the one that marks you.
What it is
Lossy compression permanently removes data judged less noticeable — JPEG, MP3. Lossless compression encodes data more efficiently with no loss, so the original can be reconstructed exactly — PNG, FLAC, ZIP.
Where it applies
GCSE and A Level computer science.
How it works
Lossy achieves much smaller files and is used where small imperfections do not matter. Lossless is required where they do — text, code, medical images, archives.
Run-length encoding and Huffman coding are the standard lossless examples taught.
How to use it in your work
Justify the choice for a given scenario. "Lossless, because the source code must be identical when decompressed."
Never say lossless "loses less". It loses nothing, and that phrasing costs the mark.
Where to get help
Your teacher and your board's specification — the pseudocode and the required language differ between boards. Bitesize covers the concepts; the computer science song runs the topics.
Revise this with a song
These are ours. We write revision songs because a lot of people remember a tune when they cannot remember a page, and because revising out loud in the kitchen beats staring at a highlighter.
- The Computer Science Song The GCSE computer science topics, set to music.
Where to read more
Last reviewed 2026-08-28 by Fiducia Together · Next review due 2027-08-28
Please note: This page explains a word or a process in education. It is general information about the system, the law and the guidance in England — not advice about your child, your school or your exam. If a decision is going against you, get advice from one of the free services we link to before you agree to anything or miss a deadline. If you are revising, check your own exam board's specification: boards word things differently and yours is the one that marks you.