Computer assisted translation applications, or CAT tools for short, are computer applications that automate routine translation operations, freeing up time for intellectual work of the translator. Unlike with machine translation, where human involvement is limited to loading a dictionary and editing the resulting text, the translation process with the use of CAT tools is constantly and entirely controlled by the translator.
By automating routine operations, CAT applications reduce the volume of manual labor involved in a translation project, speeding up the process and minimizing the cost. Automation tools help avoid the need to re-translate identical or similar text fragments that had been translated previously and are stored in the so-called translation memory, or TM for short. Translating a frequently occurring text segment once causes the CAT application to insert the translation automatically the next time you come across it. CAT tools accumulate bilingual pairs of source and target text in the TM. When you work on texts from the same subject area, the translation process picks up speed as your TM grows.
Operating Principles of Modern CAT Tools
Consider the operation of a CAT application that uses translation memory.
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The application splits the source text into segments, usually sentences or sentence fragments, and the translator types the translation of each segment directly under the source text or, if the text appears as a bilingual table, in the right-hand column.

- Segment translation is saved alongside the original text. Translator name and translation date are also stored, which is essential in team projects. You can return to any segment at any time to review or edit your translation.
- The application stores the segment in translation memory, so the next time it occurs in the source text again, the translation will be inserted from the TM automatically. CAT tools also come with a fuzzy match search feature: they detect segments that partly match previously translated segments (for example, 75% matches) and show them to prompt the translator.
Many CAT tools support integration with terminology bases enabling an automatic search and insertion of glossary term translations. Sometimes this is accomplished using add-on modules or applications, such as Multiterm for Trados.
Besides integration with translation memory and glossaries, modern CAT tools also support translation quality check modules, handle metadata (html markup tags and other tag formats), and perform other helpful functions.
Most CAT applications let you check the spelling with the use of either built-in tools or the connectible spellcheck module of MS Word. Most mainstream CAT tools come with text alignment modules that segment parallel texts into source and target segments and generate translation memory on their basis.
Files of most common text editors and layout and publishing tools (Office files, RTF, HTML, etc.) can be converted into formats supported by CAT tools. For convenience, almost all CAT applications group translation files, TM bases, and glossaries into separate projects.
Advantages of Using CAT Tools
The benefits of CAT applications are hard to exaggerate. Besides speeding up the translation process, they make it cheaper. A constantly growing TM base ensures consistent terminology and style, thus enhancing the quality of the resulting text. Translation quality is further enhanced by integration with glossaries, while many CAT applications also incorporate formal quality check tools showing whether the translation conforms to the glossary and whether the recurring segments have been translated consistently.
Using translation memory and CAT tools is essentially the only way to ensure translation consistency in large translation projects relying on a team of translators and editors.