# Computing - Compression

> Source: https://ollybritton.com/notes/a-level/computing/topics/compression/ · Updated: 2020-10-16 · Tags: computing, school, safe-to-post-online

##### Why is compression needed??
Because data is constantly being moved around computer systems and networks so a smaller amount of data can be beneficial.

##### What are the two types of comression??
* Lossy
* Lossless

##### What's an example of a lossy image compression format??
JPG

##### What's an example of a lossy music compression format??
MP3

##### What is the definition of run length encoding??
A basic method of compression that summarises consecutive patterns of the same default.

##### When does RLE work best??
Image and sound data where data is repeated many times.

##### What is dictionary compression??
Where regularly occuring data is spotted and stored in a seperate dictionary. Data is then replaced with a reference to the dictionary.

##### What is the overhead of dictionary compression??
The dictionary also has to be stored.

---
Olly Britton — https://ollybritton.com. Machine-readable index: https://ollybritton.com/llms.txt