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A bak file or .bak file is a file with extension .bak that signifies it is a backup file or, often, a duplicate of another file that is stored in a secure storage location for backup and recovery. This common format is used by many different types of software systems, including word processing and office software, design software applications and more.
A .bak file may be used in many different contexts. In some cases, they are part of an autosave feature on software that ports these temporary files to a secure location if the system encounters unexpected difficulties. These files can also be created manually, where users go in and make changes to the file extension. Alternately, a system can regularly archive large sets of .bak files for general backup purposes.
Although .bak file use can be an effective system of backup, there are some concerns with the storage strategy. The creation of .bak files can lead to "hard drive bloat," where a lot of duplicate files take up too much storage space. Another problem with .bak files is that, unlike with many of the original files, users cannot immediately determine which file type a file is. There is a reason why the three-character extensions on files are unique for every single format of file. Sometimes backup strategies make these files too generic, and make it extremely difficult to determine, for instance, if a file is a document, a video, an executable or some other type of format.