TR-Dos is complete pish, but it's incredibly popular because every
Spectrum clone in Russia (more or less) has a Betadisk interface built in.
BS-Dos is infinitely better (I imagine, never used it myself) because it
was written about 10 years later and runs on a flashy expensive disk
system, but nobody in Russia uses it because they aren't interested in
flashy expensive disk systems that aren't compatible with the TR-Dos
standard that came out 10 years earlier.
<forrest-gump>And that's all I have to say about that.</forrest-gump>