Bad Sector

A bad sector signifies a defect with the hard disk drive. When bad sectors surface the hard disk drive needs to be replaced. The small surface on a hard drive or a floppy is called a sector. The hard drives consist of numerous platters; these platters are the disks that are enclosed in magnetic material. Single platters form a floppy disk. The platters are segregated into a concentric ring sets known as tracks. There are 160 tracks in single floppy that is 1.44MB in size while a hard disk drive has thousands of tracks. The sectors are the smaller storage areas that are divisions of the tracks. The hard drives consist of millions of such sectors and it is not alarming to have bad sectors even when they are manufactured. A few sectors go bad in the lifetime of a hard drive; though they cannot be repaired they can be indicated as unusable. The data in the bad sectors can get lost but the hard disk can still be read and used. Once the sector has been indicated as unusable, the OS does not store any data in such sectors. The bad sectors reduce the storage capacity of the hard disk. . Because of a defective hard drive bad sectors are created and can spread so it is advised that a back up of the hard drive be made immediately.
The bad sectors can be repaired on a Windows XP operating system in the following manner-

• Go to Start
• Choose My Computer
• The disk that has to be scanned should be highlighted under Hard Disk Drives
• The next step is to click open the Tools window
• Select the ‘Check Now’ button

The previous versions of Windows and DOS had the function built into the utility tools of ‘scandisk’ and ‘chkdsk’. Once repaired the hard drive should be backed up regularly since the drives are mechanical devices and are prone to crashing.

Scandisk attempts to patch a bad sector once it is found, and the method is known as hot fixing or hot patching. The running of the check function of scan disk i.e. the command ‘/CHECKONLY’ identifies the bad sector but does not try to fix it. The process of hot fixing is to take the file that has the bad sectors and trying to recover all the data that is readable. The data that then is present in the bad sector is replaced with ‘zero’ as a symbol of emptiness. For instance if the clusters 5,6, 7, 8 is occupied by a file and the sector six has a number of bad sectors, the scandisk function retrieves the readable data and moves it to a new cluster say 9. The other corrupted data that is unreadable is replaced with zeros in cluster 9. The File Allocation Table for file chain is then brought up to date and cluster six is marked as a bad sector. The file then occupies a new set of cluster namely 5, 9, 7 and 8 but the lost data is not recovered by scandisk and remains empty. This is how scandisk attempts to fix the bad sectors.

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