TAR file extension is most commonly associated with an uncompressed archive created by the tar utility, and are most often found on UNIX-based operating systems. TAR files are usually used in conjunction with another utility such as GZIP or BZIP, which will be used to compress the archive to reduce the file size.
TAR files were originally developed for use with sequential backup systems such as tape. Whilst this allows the creation of TAR files from any stream of data input, it does mean that extracting single files is slow as the entire archive must be read through. TAR files, otherwise known as tarballs, are commonly used for backup purposes or to package files for distribution, and will retain the original file and folder structure once extracted. Usually, TAR files are compressed using an additional utility such as gzip or bzip to save space, and will have either a File extension TGZ or File extension TBZ file extension. This means that the file is an archive which has been created with the tar utility then compressed using either gzip or bzip2. These are equivalent to ZIP or RAR files found commonly on Windows systems.
TAR files are simply a packaged file and folder structure, and as such can be used to store data of any kind. Usually, TAR files contain backups of data or applications which have been packaged for distribution over a network, and whilst files within an archive are not run on extraction, caution should be used when opening archives from unknown sources as the contents could potentially be malicious. Additionally, poorly or maliciously created archives, sometimes called tarbombs, can dump files in the current directory, or overwrite important files in other directories on extraction. This can be inconvenient at best or at worst destructive if key files are overwritten, which is another reason to be wary of opening TAR files from unknown sources.
You can open TAR files by the majority of archiving utilities such as WinZip, 7-Zip, WinACE and Stuffit, the latter of which is available on both the Windows and Mac platforms. Alternatively, a TAR file can be extracted on any UNIX-based system from a shell prompt using tar -xf, which will restore the original file and folder structure. Alternatively, tar -tf can be used, which will display the paths to which files and folders will be extracted. This can be used to identify whether or not an archives contents are malicious or could cause a problem by overwriting existing files.
For more general information about files, file extensions and registry you can read one of the following articles:
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