Microsoft KB Archive/69579

CHKDSK Can Fail on 1.44 MB Floppy Disk PSS ID Number: Q69579 Article last modified on 07-14-1993 PSS database name: O_MSDOS

3.x 4.x

MS-DOS

Summary:

When the MS-DOS CHKDSK utility is run on a 1.44 MB, 3.5-inch floppy disk that contains both cross-linked files and a volume label, CHKDSK may report incorrect errors or lock the system.

To work around this problem, use the MS-DOS LABEL utility to remove the volume label, then run CHKDSK.

More Information:

When CHKDSK discovers a cross link error in the file allocation table (FAT), it attempts to find the two files that own the cross-linked chains. Due to an error in CHKDSK, it attempts to traverse the nonexistent chain owned by the volume label. Because the starting cluster entry for a volume label is always set to zero, CHKDSK tries to interpret the first entry in the FAT as a valid cluster entry. On all disk types except for 1.44 MB, this location (the media descriptor) is equivalent to an end-of-chain entry, and CHKDSK stops. On a 1.44 MB disk, however, the number stored in the media descriptor field is a valid cluster number (0xFF0), and CHKDSK attempts to follow the chain. This can lead to an infinite loop, or incorrect results, depending on what is located in the memory CHKDSK attempts to access.

Microsoft has confirmed this to be a problem with MS-DOS versions 3.3 through 4.01. This problem does not occur in later versions of MS-DOS.

Additional reference words: 3.30 3.30a 4.00 4.01 noupd

Copyright Microsoft Corporation 1993.