Microsoft Knowledge Base

• Microsoft MS-DOS operating system versions 6.2, 6.21, 6.22

1. Q. What does ScanDisk do?

   A. ScanDisk detects, diagnoses, and repairs disk errors on
      uncompressed drives and DoubleSpace compressed drives. ScanDisk
      can repair file system errors such as crosslinked files and lost
      clusters as well as physical disk errors.

      ScanDisk keeps a log of the repairs it makes and allows you to
      undo any of the changes it makes. When you compress a drive,
      DoubleSpace runs ScanDisk to check the reliability of your disk
      before it begins compressing the drive. You can also run
      ScanDisk yourself by typing "scandisk" (without the quotation
      marks) at the MS-DOS command prompt.

      For more information, type "help scandisk" (without the
      quotation marks) at the MS-DOS command prompt and then press
      ENTER.

2. Q. ScanDisk found and repaired an error on my hard disk drive
      during the surface scan, but not all of the affected file was
      fully recovered. What happened to my file?"

   A. When ScanDisk encounters a bad sector in a file, it repairs the
      file by mapping in a new sector. Because the data in the
      original sector is unreadable, ScanDisk fills the new sector
      with zeros. This repair makes the file fully readable, but any
      data that was in the defective sector is still lost.

      If you have a data file that was repaired by ScanDisk, your
      application usually can read most of the file. If a program file
      was repaired, you should restore the file from the original
      program disks. For more information, contact your software
      vendor.

3. Q. Why does ScanDisk perform a surface scan on my compressed drive
      when it has just finished scanning the host drive? Is it really
      necessary to perform a surface scan on both drives?

   A. There is a difference between a surface scan on a compressed
      drive versus a host drive. To thoroughly check the drives, the
      surface scan should be performed on both the compressed drive
      and its host.

      When ScanDisk performs a surface scan on a uncompressed drive,
      it is checking the physical integrity of each sector on the
      drive. When ScanDisk performs a surface scan on a compressed
      drive, it is verifying the data on the drive can be uncompressed
      without error.