chkdsk.exe

Chkdsk.exe in action on drive C:
Original author(s)	Microsoft
Operating system	MS-DOS and NT-based versions of Windows
Platform	x86 and x64 (Windows [XP Professional, Vista, & 7] x64)
Available in	Multilingual
Type	System tool
License	Commercial (part of MS-DOS and Windows).

CHKDSK (short for "check disk") is a command on computers running DOS, OS/2 and Microsoft Windows operating systems that displays the file system integrity status of hard disks and floppy disk and can fix logical file system errors. It is similar to the fsck command in Unix.

The command is implemented as an executable program file, CHKDSK.EXE. Different operating systems all use the same filename, but the files are not necessarily compatible between operating systems.

On computers running NT-based versions of Windows, CHKDSK can also check the disk surface for physical errors or bad sectors, a task previously done by SCANDISK. This version of CHKDSK can also handle some physical errors and recover data that is still readable.

Windows NT-based CHKDSK[link]

CHKDSK can be run from the Windows Shell, the Windows Command Prompt or the Windows Recovery Console. One option for CHKDSK is the use of the Command-line /R parameter, which allows the program to repair damage it finds on the hard drive.

Conducting a CHKDSK can take some time, especially if using the /R parameter, and the results are often not visible, for various reasons. The results of a CHKDSK conducted on restart using Windows 2000 or later operating systems are written to the Application Log, with a "Source" name of Wininit or Winlogon and can be viewed with the Event Viewer. On the Windows 7 operating system, the events have a "Source" name of "Chkdsk"

The standard version of CHKDSK supports the following switches :

When running CHKDSK from the Recovery Console the options are different. The /p is not read-only as in the standard version but corrects errors :^[1]

A typical result:

Checking file system on C:
The type of the file system is NTFS.

A disk check has been scheduled.
Windows will now check the disk.
Cleaning up minor inconsistencies on the drive.
Cleaning up 318 unused index entries from index $SII of file 0x9.
Cleaning up 318 unused index entries from index $SDH of file 0x9.
Cleaning up 318 unused security descriptors.
CHKDSK is verifying file data (stage 4 of 5)...
File data verification completed.
CHKDSK is verifying free space (stage 5 of 5)...
Free space verification is complete.

  14996645 KB total disk space.
  10187752 KB in 88054 files.
     30784 KB in 5774 indexes.
         0 KB in bad sectors.
    164341 KB in use by the system.
     65536 KB occupied by the log file.
   4613768 KB available on disk.

      4096 bytes in each allocation unit.
   3749161 total allocation units on disk.
   1153442 allocation units available on disk.

Vista result (App Event Log) found in "bootex.log" in the root folder of the drive:

Checking file system on C:
The type of the file system is NTFS.

A disk check has been scheduled.
Windows will now check the disk.                         
  79232 file records processed.
  332 large file records processed.
  0 bad file records processed.
  2 EA records processed.
  44 reparse records processed.
  105198 index entries processed.
  0 unindexed files processed.
  79232 security descriptors processed.
  Cleaning up 1 unused index entries from index $SII of file 0x9.
Cleaning up 1 unused index entries from index $SDH of file 0x9.
Cleaning up 1 unused security descriptors.
  12984 data files processed.
CHKDSK is verifying Usn Journal...
  35789792 USN bytes processed.
Usn Journal verification completed.
Windows has checked the file system and found no problems.

  78175231 KB total disk space.
  12902428 KB in 54029 files.
     36068 KB in 12985 indexes.
         0 KB in bad sectors.
    187407 KB in use by the system.
     65536 KB occupied by the log file.
  65049328 KB available on disk.

      4096 bytes in each allocation unit.
  19543807 total allocation units on disk.
  16262332 allocation units available on disk.

DOS-based CHKDSK[link]

This section requires expansion.

The MS-DOS 5 bug[link]

The version of CHKDSK (and Undelete) supplied with MS-DOS 5.0 has a bug which can corrupt data. This applies to CHKDSK.EXE and UNDELETE.EXE with a date of 04/09/91 (April 9, 1991). If the file allocation table of a disk uses 256 sectors, running CHKDSK /F can cause data loss and running UNDELETE can cause unpredictable results. This normally affects disks with a capacity of approximately a multiple of 128 MB. This bug was fixed in MS-DOS 5.0a. A Microsoft Knowledge Base article^[2] gives more details on this.

See also[link]

• Defragmentation
• Fsck

External links[link]

• Microsoft
  • Microsoft TechNet Chkdsk article
  • Understanding what CHKDSK does (NTFS only) – Microsoft Article
  • Troubleshooting Disks and File Systems - TechNet Article on Windows XP resources to troubleshoot hard disk errors
• Other
  • Graphical CHKDSK Walkthrough – Covering both Windows and Command line options
  • How to Use Chkdsk in Windows XP – Also explains how the program works

References[link]