Workbook on Digital Private Papers > Glossary
Glossary - C
Compression
To compress is to shrink one or more files into a single file which requires less storage space than the original. Compression is achieved by using algorithms (a popular example is the ZIP file format), which must also be used to uncompress the file if it is to be displayed or used. Essentially, the algorithm looks for patterns in the data and substitutes these with smaller patterns based on the algorithm's conventions. The degree to which a file can be compressed is dependent on the patterns which the alogorithm can locate. Advantages of compression include the speed at which a compressed file can be sent through the Internet and reducing storage space. Compression is lossless where the encoding is reversible and the original data can be reconstructed exactly (e.g. ZIP); compression can also be lossy (e.g. saving a high quality TIFF as a JPEG). Compression also allows a number of files to be zipped together and treated as one entity for the purpose of creating a checksum which can be used by a digital archivist as a means of checking the authenticity of a digital accession.
