A translation memory is in its simplest form a database where a translator may record old translations for future reuse and easy searches. Although these programs are best classified undercomputer-aided/assisted translation, one must not confuse them with machine translation programs - translation memory software does not translate anything by itself, whereas a machine translation system actively produces language and translations based on linguistic data,such as grammatical rules and glossaries. A translation memory systemleaves all the actual translating to the human translator.
Basically, translation memory records sentence pairs: a source languagesegment (usually a sentence) is combined together with a target language segment. If an identical (or similar) source language segment comes up in another translation later, the translation memory program will find the previously translated segment and suggest it as the basis for the new translation. The suggestion may be either approved as it is, edited to match the current situation or rejected entirely. Most programs use a "fuzzy matching" algorithm, which makes the programs ever moreuseful; searches will find not only hundred per cent matches but also segments that only resemble the search phrase to a certain extent. There are a great deal of similarities between the various softwarepackages. It is possible to search not only for full segments, but also single words or phrases, which helps the translator to find terminology and keep the text consistent. Also, there is usually an interface to aterminology management program - usually the manufacturer's own,sometimes third-party programs too.
There are translation memory programs that work together with machine translation software as well. Some work directly within an existing word processor, others (most) have their own editor. All of these packages feature filters for importing andexporting various file formats. Most, if not all, also provide an alignmenttool for adding older translations (not done with the software) into thememory for reuse.