You don´t need a S50 formatted disk...
If you´re using a PC, get both SDISK program and the OS file from Roland U.S. site, and use a DOS formatted disk. (Just remember to quit Windows, to DOS mode, before using SDISK...).
I don´t know if Mac uses its own formatted disks, but Roland site provides Mac files as well.
Look at:
http://www.rolandus.com/SUPPORT/SOFTWARE/PCSAMP.HTM for PC files and
http://www.rolandus.com/SUPPORT/SOFTWARE/MACSAMP.HTM for Mac files.

Mgomes