Compression: Computer Science OCR: GCSE (9:1)

Compression

Decreasing the size of a file by removing unnecessary data or storing the data in an alternative way

Run Length Encoding

Compression algorithm which stores "runs" of consecutive values in number value pairs. So AAAABB could become 4A2B

Lossy

A type of compression algorithm which makes a file smaller by permanently removing data, so data from the original file is lost and cannot be recovered, e.g. MP3, JPEG

Lossless

This type of compression algorithm shrinks a file by reorganising data without losing any, such that it can later be restored to its original state with identical quality, e.g. ZIP, RLE.

Storage

Anywhere a computer stores data. Space here is always limited, so we sometimes compress data to save space

Bandwidth

The amount of data that can be transmitted over a network in a given amount of time, or the speed of a network. Because this is limited, we sometimes compress files before transmitting

Streaming

Process of downloading compressed music or video over the internet, in a continuous and even flow. Uses compression to save bandwidth

Archive

We often zip up our files in one of these, to save space

JPEG

A commonly used file format that uses lossy compression for digital photography

MP3

A standard format for music files stored on music players or sent over the internet that compresses music data to reduce the file size

Document

File type containing text, it should never be compressed using a lossy technique, because every character is important. Lossless is more suitable

Image

A file containing this type of data is usually suitable for lossy compression because even if we lose some of the data the content is still usable

Artifact

Lossy compression can create these, it means an unwanted feature added to the file by the algorithm, such as echos and squeals in MP3 audio