Short answer: SR-77 is derived from S-7 tool steel. SR-101 is derived from 52100 Ball bearing steel. S-7 is probably the tougher steel and 52100 probably has a slight advantage in edge retension.
OK, I lit the dynamite <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />
Kraz, thanks, thats the kind of layman terms I can digest, but don't quiz me on it later!