Memory and storage Revision Notes

What is Data Compression?

Data compression is the process of encoding information using fewer bits than the original representation. The main goals are to reduce storage space requirements and speed up data transmission. Compressed data needs to be decompressed to be used. The method chosen depends on the type of data and what it will be used for.

Lossless Compression

Lossless compression reduces file size without any loss of data. When decoded, the exact original data is recovered. This is vital for files where any alteration would be detrimental, such as text documents, software applications, and certain image formats (e.g., medical scans). Common examples include RLE (Run Length Encoding) and Dictionary-based methods like LZW, used in formats like ZIP, PNG, and GIF.

Lossy Compression

Lossy compression achieves greater file size reduction by permanently removing some data. This discarded information is usually less significant or imperceptible to human senses. The decompressed file is an approximation of the original, not an exact copy. This method is effective for multimedia files like images (JPEG), audio (MP3), and video (MPEG), where a slight decrease in quality is an acceptable trade-off for significantly smaller file sizes, enabling faster streaming and downloads. The level of compression can often be adjusted, balancing file size against perceived quality.

Advantages and Disadvantages

Advantages of compression include reduced storage space, faster transmission speeds over networks, and lower bandwidth requirements. For example, a compressed image takes less time to upload. Disadvantages can include the time and processing power required to compress and decompress files, and with lossy compression, the irreversible loss of data quality. Incorrectly chosen compression methods can lead to corrupted or unusable files.