Translation memory

A translation memory, or TM, is a database that stores "segments", which can be sentences, paragraphs or sentence-like units that have previously been translated, in order to help human translators.
The translation memory stores the source text and its corresponding translation in language pairs called “translation units”.

Software programs that use translation memories are sometimes known as translation memory managers (TMM); or translation memory programs
Software programs that use translation memories are sometimes known as translation memory managers (TMM); or translation memory programs

The program breaks the source text (the text to be translated) into segments, looks for matches between segments and the source stored in a translation memory, and presents such matching pairs as translation candidates. The translator can accept a candidate, replace it with a fresh translation, or modify it to match the source. In the last two cases, the new or modified translation goes into the database.
How do the translation memory programs work?

Some translation memories systems search for 100% matches only.
That means that they can find only those segments of text that match entries in the database exactly, while others employ fuzzy matching algorithms.
Fuzzy matching algorithms
Fuzzy matching is the technique of finding matches that match a pattern approximately (rather than exactly).

Translation memories work best on texts which are highly repetitive, such as technical manuals. They are also helpful for translating changes in a previously translated document, corresponding, for example, to minor changes in a new version of a user manual.
Traditionally, translation memories have not been considered appropriate for literary or creative texts, for the simple reason that there is so little repetition in the language used

Main benefits:
Ensuring that the document is completely translated (translation memories do not accept empty target segments)
Ensuring that the translated documents are consistent, including common definitions, phrasings and terminology. This is important when different translators are working on a single project.
Accelerating the overall translation process; since translation memories "remember" previously translated material, translators have to translate it only once.
Reducing costs of long-term translation projects

Main obstacles:
A guiding principle of translation is that the translator must translate the message of the text, and not its component sentences. And its difficult to make a computer understand the message of a text.
Translation memory managers do not presently support all documentation formats
Full versions of many translation memory managers can cost from $500 to $2,500
Sometimes usability and quality of TM matches are decreased due to the fact that the maintenance of translation memory databases still tends to be a manual process
The quality of the text recorded in the translation memory is not guaranteed

History of translation memories
In 1970s there was an infancy stage for TM in which scholars carried on a preliminary round of exploratory discussions.
The original idea for TMS is often attributed to Martin Kay's "Proper Place" paper
Another people named Alan Melby and his group at Brigham Young University were also claimed to be the founding father of TM
The real exploratory stage of TMS would be 1980s. One of the first implementation of TMS appeared in Sadler and Vendelmans' Bilingual Knowledge Bank
The aim of Bilingual Knowledge Bank is to develop a corpus-based general-purpose knowledge source for applications in machine translation and computer- aided translation
TM technology only became commercially available on a wide scale in the late 1990s