On one of my (older) computers there is a defect sector on the hard disk.
Checking the surface of the hard disk shows a red square for it.
It seems to me that all the "usual" reserve sectors are already in use.
Every thing else works on this computer. No unusual noise comes from the hard disk...
backup
bad sectors
data recovery
defect sector
disk check
disk utility
diy tech
dummyfiles
file management
file system
hard drive
old computer
sata
sector identification
storage issues
surface test
system repair
windows 7
write protection