This is the best I can find in a pinch. It's possible it reads at the sector level and repairs at the bit level. It's been awhile since I've been knee deep in Steve's ass and testimonials. Old Security Now episodes have a lot of info on how it works.

https://www.grc.com/sr/faq.htm

Data recovery companies work the hardware which can be a point of failure. Spinrite tries to recover the data before the hardware fails. The greater density a disk has, the more failures are expected and error correction just assigns bad sectors as they fail. Between that and the OS, my understanding is that the slow degradation of a drive is managed until it can't be. Even running Spinrite on a new drive is beneficial because new drives come with bad sectors. By assigning them as bad up front you get ahead of bad sectors and even can catch a lemon before it crashes. I've recovered unreadable drives with Spinrite. It's impressive. It doesn't solve all issues, but it's really good.