Year11 - Compression Starter

Why We Use Compression

Practise the key ideas of lossy and lossless compression from OCR GCSE (J277).

Today’s Big Idea

Compression reduces file size to save storage space and speed up transfer. The method depends on whether data can be lost.

Lossy vs Lossless

Activity 1: Match Compression Terms

Drag each term to its correct meaning.

Compression
Lossy compression
Lossless compression
Faster transfer
Images / sound / video
Text / executable files
Term Meaning
Reduces the number of bits used to store a file.
Removes some data permanently to reduce file size more.
Keeps all data so the original file can be restored exactly.
A key benefit of smaller files when sending or streaming.
Commonly suitable for lossy compression when some quality loss is acceptable.
Must use lossless compression to avoid losing essential data.

Activity 2: Build the Compression Decision

Put the steps in order for compressing a code file while keeping it usable.

Transfer the smaller file more quickly.
Choose lossless compression (no data loss).
Decompress back to the original exact file.
Identify it as a text or executable file.
Compress by encoding data differently.

Step 1

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Step 2

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Step 3

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Step 4

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Step 5

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Activity 3: Choose the Best Method

Scenario: A school website stores student profile photos and exam software installer files. Explain which compression method fits each and why.

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