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Microsoft KB Archive/103956

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Knowledge Base


How ScanDisk Fixes Bad Sectors

Article ID: 103956

Article Last Modified on 11/19/1999



APPLIES TO

  • Microsoft MS-DOS 6.2 Standard Edition
  • Microsoft MS-DOS 6.22 Standard Edition



This article was previously published under Q103956

SUMMARY

When ScanDisk encounters a bad sector it attempts to patch the sector. This is known as hot fixing or hot patching.

NOTE: If you are running in check mode (/CHECKONLY), ScanDisk does not attempt to hot fix the bad sectors.

MORE INFORMATION

Hot patching is the process of taking a file that contains one or more unreadable (bad) sectors and recovering all the data that is still readable. Any data that lies in a bad sector is replaced by zeros.

For example, if a file occupies clusters 1, 2, 3, 4, and 5, and cluster 3 contains one or more bad sectors, ScanDisk reads as many of the sectors from cluster 3 as possible and moves the data to a new location (for example cluster 7). Any sectors from cluster 3 that could not be read are replaced with sectors filled with zeros in cluster 7. The FAT chain for the file is updated and cluster 3 is marked bad. After this process is finished, the file occupies clusters 1, 2, 7, 4, and 5.

NOTE: This process makes the file fully readable, but the data that was in the defective sectors is still lost. It is not possible for ScanDisk to recover data from unreadable sectors.


Additional query words: 6.20 hotfix hotpatch hotfixes hotpathes scan disk

Keywords: KB103956