I have just posted this video on YouTube in order to share it here and on my Spinrite product page on the Fact-Reviews site. Steve Gibson explains what Spinrite does and how it operates, including how it "begs" for data from dodgy areas of the disk in order to recover it.
He also mentions the concept of "Bit Rot", where the defects on a hard drive can grow over time, gradually affecting more bits in a sector, until the sector becomes unreadable. Fortunately DiskFresh can also help detect these problems early without taking the entire PC offline for maintenance. With Spinrite the entire PC has to boot off a special boot CD or flash drive in order for Spinrite to do the recovery.
Of course if the PC isn't booting up anyway this is not really an issue, but with preventive maintenance it can be a big issue. That's why I was delighted when DiskFresh was developed, because now I can find out whether my hard drives (including removable USB drives) are developing problems before it is "too late".
Another issue I was not aware of is when and how often drives fail, including brand new "out of the box" drives. The authors of "Protecting Digital Assets for the Long Term" cite research from Google and others which suggests that new drives should be tested between 200 and 2000 hours before being put into active service, to prevent what they term "infant mortality" failures. The problem gets bigger as the size of the drive gets bigger, too.
It is also not a good idea to leave a drive switched off for too long, because the mechanism can get stuck and the drive may never spin again. If you are using an external hard drive for backups, make sure you do a regular backup (monthly is more than adequate) to that drive, just to make sure that the drive is still working properly. And remember to do your quarterly disk refresh with DiskFresh (see article below).