Recommended Commercial Software – SpinRite from Gibson Research
SpinRite is a program that I have used for decades, literally, to maintain magnetic data integrity and to diagnose and attempt recovery from surface errors.
By booting to a SpinRite CD or USB flash drive, bypassing Windows, the program has low-level access to your drive. USB and Firewire drives are not accessible.
The only problem is that SpinRite needs to be updated for the larger capacity drives of today. I cannot say for certain what the cutoff is, but for older drives, SpinRite has proven itself to me many times. Now when they update it, I’ll shout it from the rooftops!