NewDeal Technical Support Document 248


How to check your hard drive for bad sectors, and how to repair them

Occasionally any hard disk can develop minor surface defects which can cause problems with your data. If your programs suddenly start giving you error messages, or crashing without error messages, and you haven't changed your computer's configuration, you might have damaged sectors. The bad sectors are usually easy to find and fix.

Damaged sectors are sometimes called "check disk errors," named so after the DOS program CHKDSK, which can sometimes be used to locate them.

Commercial Hard Disk Utility Programs

The best way to find and fix bad sectors is to use a commercial hard disk utility program, such as Norton Disk Doctor, PC Tools' Disk Fix, or Microsoft's ScanDisk. There are many other products available for the same purpose. If you use a commercial hard disk repair program, follow the instructions in the program's manual for finding and repairing the damage. Then go to "The Final Step" section below.

Finding Damaged Files using CHKDSK

If you don't own a hard disk utility program, you can use the DOS command CHKDSK to find and repair some file errors. However, keep in mind that commercial disk checking programs have a higher success rate for finding and repairing damaged files. Also, be aware that CHKDSK cannot find or repair physical defects on the disk, CHKDSK can only locate problems with the file directory structure.

To check for damaged files with CHKDSK, exit any programs you have running. At any DOS prompt, enter

If CHKDSK finds errors, it will report them with a message like "Errors found" or "Cross-linked files."

If CHKDSK prompts you to "Convert lost chains to files?" enter Y. DOS will convert the information stored in the damaged files into files with the file name extension CHK. You can delete these files later if you don't want to try to recover information from them.

Fixing Cross-Linked Files

CHKDSK cannot fix files that are cross-linked. To fix them, you must delete every file that DOS reports as being cross-linked. After you delete the files, run CHKDSK /f again.

If CHKDSK Didn't Find Any Problems

CHKDSK may give your hard disk a clean bill of health even if there are bad sectors. This is because CHKDSK can only find files that have been mis-allocated, it cannot find all physically damaged sectors. If CHKDSK shows no errors, try installing the software program that's crashing into a new, different directory. Then run the program from that directory. If the program no longer crashes, the other copy of it may be stored on bad sectors.

The Last Resort

Before the existence of hard disk utilities like Norton DiskDoctor or ScanDisk, we used the FORMAT command to thoroughly test a hard drive and either repair or block off bad sectors. CAUTION: FORMAT erases all the files on your hard drive, both document files and program files!

Before you reformat a drive, make a backup copy of all your files on floppy diskettes, on tape, on removable disks, or an other hard drive. In the absence of a hard disk utility like DiskDoctor or ScanDisk, you can eliminate bad sectors by backing up all your files, reformatting the drive, and then restoring all your files from the backup. If any of the files you backed up were stored on bad sectors, they may still be corrupt, so proceed to the final step.

The Final Step

After making sure that your drive has no bad sectors, if a file -- either a program file or one of your personal documents -- was stored on a damaged sector, you will probably have to restore the file from a backup, or re-install the software program that contains that program file. It may be difficult to tell which files were on the bad sectors. After you've fixed the errors, try to run your programs and re-install any programs or documents that misbehave.
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Last Modified 17 Feb 1999