What is a r21 file and how do I open a r21 file?

The R21 file extension was developed by Eugene Roshal and it is attached to WinRAR Split Archive Part 21 or files that are compressed and belong to the multi-volume compressed .RAR archive parts. These files are the 21st part of the archive that’s been compressed and split in order to fit into multiple discs either for backup purposes or to transfer to another computer, etc. These R21 files are useful when it comes to the reconstruction of original files together with other parts of the split archive. R21 may not be the last part of the split archive files as RAR multi-volume archives could reach up to R99. The number after the letter R in this file extension actually represents the sequence or the part of the split archive. There are a number of archivers that can be used to open R21 files and Whirling Dervishes Alpha ZIP was added to the list as well as Smith Micro StuffIt Deluxe 2011. 

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