That is..

Often enough the base format magn. domains have migrated radially with wear, time.. reducing output to read-head. Eventually enough that CRC retries won't make it.
Not necessarily really 'BAD' sectors at all. SR moves all the data for each cyl, then redoes a low-level format -- where the head actually is now, etc. Also 'scrubs' adjacent bits, really pretty close to an authentic B/H curve check!

Has a statistical recovery mode which makes mondo passes, where the data doesn't 'seem' to be quite there anymore: and a cute display for the Gamers -- of how it's doing.

Pretty amazing stuff; from a physics perspective - it ain't no snake oil. I've seen lots of B/H curves.. Steve Gibson may not make the Top Ten here, for his Barnum pitches to the unwashed -- but I think SR is amongst the cleverest pieces of mere 'software' I've ever encountered.


Luck