tomatthe :
It does not repair them, things that say they repair them basically just mark them as bad sectors so they are no longer used. If you have a drive with bad sectors, replace it or use it under the expectation all data on it may be lost at any point in time.
I've got an IBM Thinkpad laptop with a Hitachi Travelstar 7K60 hard drive which stopped booting Vista. So I booted into safe mode cmd prompt with the Vista disc and ran "chkdsk /f" which reported and repaired errors. But I still could not boot from the hard drive, so I booted off the disc and ran "chkdsk /r" which also reported and repaired errors. I think it said it detected bad sectors and moved the data from these sectors. When I tried to boot from the hard drive once more, no success. So I booted of the disc and let it try to solve startup problems which reported errors with the hard drive. I repeated this process a few times as the laptop would not start from the hard drive. Eventually, chkdsk told me:
"The disk does not have enough space to replace bad clusters detected in file 5349 of name ."
Did some online research and the best explanation I could find was that the unallocated sectors reserved as replacement for bad sectors on the drive was all used up. Too many bad sectors it seem! So I ran Hitachi's Drive Fitness Test utility which reported the drive as defective. I then tried Spinrite at level 5 which also detected bad errors and tried to recover - scanned about 1% in 8 hours. With nothing to lose, I used the Hitachi program to erase the drive which according to the manual "write zeroes to every sector of your hard drive including the boot sector". Then ran Spinrite again at level 5 which scanned the entire drive and reported no errors in about 3 hours. I was amazed....no errors!
So I tried installing XP allowing XP's installer to repartition and full format the drive. After XP installed, I ran XP's check disk (with the GUI) with the "scan for bad sectors" option. Amazingly, no errors reported! How is this possible? Is the drive really repaired?
I hope you don't mind my long story but I'm curious to know how the Hitachi disk zeroing worked this miracle.