Compression

Compression is the process of reducing the size of a file by reducing the amount of data it contains. A compressed song, poster or game level still plays, opens or works, but it takes up less room.

Why compress a file?

Every file you store or send costs space and time, and compression cuts both:

• Storage — a phone, memory card or school network drive holds far more files when each one is smaller, so you run out of room less often.
• Transfer — a smaller file uploads, downloads and streams more quickly, because there is less data to push across the connection.
• Web pages and online media — a photo-heavy page opens sooner on a weak mobile signal, a video streams with less buffering, and a podcast episode downloads faster before a journey.

What it can cost

The two main types are lossy compression and lossless compression. Lossy compression discards some of the original data, so the file can lose quality — though often you would not notice unless it is squeezed very hard. Lossless compression throws nothing away, so the original quality is kept. Which one suits a file depends on whether its exact contents must survive.

A worked example: a 300 MB project file takes 60 seconds to upload over a connection that carries 5 MB every second. Compressed to 60 MB, the same upload takes 12 seconds. The time saved by sending less data is often worth more than the space saved on the drive.