File extensions: r01, r02, r03, etc. are RAR files. The original RAR-file naming convention used three-digit extensions. When a RAR archive went over 100 segments, the “r” would change to an “s”. So after blahblahblah.r99 would be blahblahblah.s00, and then blahblahblah.s01, etc.
TechSono software uses R** to denote these old RAR files.