Article ID: 127055 - View products that this article applies to.
This article was previously published under Q127055
IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:
(http://support.microsoft.com/kb/256986/EN-US/ )Description of the Microsoft Windows Registry
By default, ScanDisk for Windows (Scandskw.exe) does not test clusters that are marked as bad in the file allocation table (FAT). This behavior applies for both compressed and uncompressed drives and is consistent with the behavior of the MS-DOS ScanDisk utility (Scandisk.exe) included with MS-DOS version 6.x and Windows 95.
You can configure ScanDisk for Windows to test clusters marked as bad in the FAT by editing the registry. This article describes this procedure and discusses why you might want to clear existing bad cluster marks in the FAT.
WARNING: This procedure could possibly prevent certain applications from functioning properly, prevent certain applications from running at all, or, in rare cases, cause partial to complete data loss. Use the procedure described below only at your own risk.
WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.
ScanDisk for Windows does not normally attempt to repair clusters marked as bad (FF7h for a 12-bit FAT and FFF7h for a 16-bit FAT) because there are many instances in which the clusters have been marked as bad for a valid reason. If a bad cluster mark is cleared in this situation, problems could arise. The following situations are examples of how clearing a bad cluster mark can cause problems:
You can force ScanDisk for Windows to retest bad clusters by modifying the value for the following registry key:
This registry key will exist only if ScanDisk for Windows has already been run. To have ScanDisk test clusters that have been marked as bad, modify the Settings value so that the last two digits are "04." For example, if the current value for Settings is
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\ Applets\Check Drive\Settings
change it to read:
B1 03 40 00
Once you modify the value for Settings, ScanDisk for Windows will retest any clusters marked as bad. If ScanDisk can correctly read a bad cluster, the following message will be displayed:
B1 03 40 04
It is important to remember that bad cluster marks on an uncompressed drive may indicate marginal media that cannot be read reliably. Letting ScanDisk for Windows clear a bad cluster mark made by another surface scan utility could result in partial or complete data loss if the cluster cannot be read reliably. Make sure to back up your hard disk before you let ScanDisk repair a bad cluster mark on an uncompressed drive.
ScanDisk found an error on <volume label> (<drive>) Cluster nnn is marked as bad, but ScanDisk cannot detect anything wrong with it. Bad clusters are physical areas of your disk that a program has identified as being unreliable for storing data. - Leave the cluster marked bad and continue. (Default) Ensures that the cluster will remain unavailable for storing data, which is the safest option. Some encryption programs, or programs that are copy protected, mark one or more clusters as bad to prevent other programs from accessing them. If you are using one of these programs, you should leave the bad cluster mark intact. - Clear the bad cluster mark. Marks the cluster available for storing data. Although ScanDisk did not detect anything wrong with this cluster, you may encounter errors if you use it. - Test the cluster again. Retests the bad cluster. If the test fails, ScanDisk will leave the cluster marked as bad and will continue searching your disk for other errors. If the test succeeds several times, it is probably safe to store data in this cluster.