Any file with a file extension of the format .R followed by a number between 00 and 99 (e.g. .R00, .R01 and .R99) is a split RAR (Roshal Archive file). RAR is a data compression, storage and transfer file format. These files can be uncompressed using a range of available programs, using the proprietary RAR algorithm, however the most common windows package is WinRAR (shareware).
An archive compressed using the RAR or WinRAR file compression programs might be divided into smaller files, which, in turn, might be labeled with the extensions .R00 through to .R99.