Nope, it's MFM. RLL and MFM are actually more or less the same stuff (if I remember it correctly), but RLL compressed the data differently so it can pack more onto the same drive. I remember running an ST-225 MFM-drive in RLL-mode on a PC and it would work for a couple of weeks and then it'll just start to use data. The ST-251 was made for RLL and MFM-use though.