How it works
A bad sector is a storage area that cannot be used reliably in the expected way. Physical-media problems and logical file-system problems are different. A drive may remap an unusable area, but remapping does not reconstruct missing file content or make the underlying device indefinitely trustworthy.
A practical example
A photograph may fail to open while other files remain readable. Repeated attempts or repair writes can reduce the chances of preserving the original readable data. First establish whether a backup exists and whether recovery is more important than getting the device back into service.
What to check
Record read errors, symptoms and the exact drive identity. Check cables and access conditions without destructive tests. Use manufacturer information to interpret indicators and protect accessible important files where safe; unstable or clicking drives need special care.
Limits and safe next steps
Formatting is not proof of healthy media. Do not run write-based repair tools before considering recovery needs. A missing warning cannot rule out a fault, and one isolated counter needs context rather than a universal interpretation.