tar The .tar filename was originally designed to be used as a TApe ARchiver to store entire file systems and files as single files on tape storage medium. It was designed by AT&T in 1979. Today, the format more commonly refers to an archive or collation of multiple files into a single file with the .tar filename extension. The format is an open source file archive format commonly associated with the UNIX tar command however other data compression tools are capable of effectively compressing and/or decompressing files saved with the .tar file format. Doing so typically adds the compression filename extension to the archive file for example .tar.bz2.
rar The .rar filename extension is a popular and partially open archive file format associated with the compression and decompression tool WinRAR. The format was developed by Eugene Roshal with its initial release in 1993. It, like many other archive formats, acts as the compressed data container for one or several files. The archive format can maintain the directory structure of the compressed archive even when unpacked to a directory. The RAR file format supports multi volume file compression where an archive is saved as a sequence of several files of a given size.