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{{short description|System tool in DOS, OS/2 and Windows}}

CHKDSK (short for "check disk") is a system tool in DOS, FlexOSweblink 4690 OSweblink OS/2 and Microsoft Windows. It verifies the file system integrity of a volume and fixes logical file system errors. It is similar to the fsck command in Unix and similar to Microsoft ScanDisk which co-existed with CHKDSK in Windows 9x and MS-DOS 6.x.


{{Expand section|date=February 2019}}


The CHKDSK command was first implemented by Tim Paterson and included in Seattle Computer Products 86-DOS.86-DOS User's Manual - Version 0.3


CHKDSK and UNDELETE in MS-DOS 5.0 have a bug which can corrupt data: 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 applies to CHKDSK.EXE and UNDELETE.EXE bearing a datestamp of April 9, 1991. This bug was fixed in MS-DOS 5.0a.WEB,weblink When Not to Use MS-DOS 5.0 CHKDSK and UNDELETE Commands, 16 November 2006, Support, Microsoft, 1.1,

Microsoft Windows

CHKDSK can be run from DOS prompt, Windows Explorer, Windows Command Prompt, Windows PowerShell or Recovery Console.WEB,weblink Description of the Windows XP Recovery Console for advanced users, 11 July 2013, 4 September 2014, Support, Microsoft, 8.0, On Windows NT operating systems, CHKDSK can also check the disk surface for bad sectors and mark them (in MS-DOS 6.x and Windows 9x, this is a task done by Microsoft ScanDisk). The Windows Server version of CHKDSK is RAID-aware and can fully recover data in bad sectors of a disk in a RAID-1 or RAID-5 array if other disks in the set are intact.BOOK, Managing and Maintaining a Microsoft Windows Server 2003 Environment, Dan, Holm, Orin, Thomas, Microsoft Press, 9780735614376, 2003, 11-3: Maintaining Disk Storage Volumes, 11.25, On Windows NT family, a standard CHKDSK scan consists of three phases of testing file metadata. It looks for errors but does not fix them unless it is explicitly ordered to do so. The same applies to surface scan—this test, which could be extremely time-consuming on large or low-performance disks, is not carried out unless explicitly requested. CHKDSK requires exclusive write access to the volume to perform repairs.WEB, An explanation of the new /C and /I Switches that are available to use with Chkdsk.exe,weblink Microsoft Support, Microsoft, 25 January 2019,weblink" title="">weblink 24 October 2014, 1 December 2007, WEB,weblink Troubleshooting Disks and File Systems, 3 November 2005, 4 September 2014, Windows XP Professional Resource Kit, Microsoft, Because of the exclusive access requirement and the time-consuming nature of CHKDSK operation, Windows Vista implemented a new file system health model in which the operating system fixes errors on the volumes as it encounters them. In the event that the problem is grave and a full scan is required, Action Center notifies the user to take the volume offline at the first convenience.WEB,weblink Redesigning chkdsk and the new NTFS health model, 10 May 2012, Building Windows 8, Microsoft, Bangalore, Kiran, Steven, Sinofsky, Windows Vista and Windows Server 2008 added self-healing ability, turned on by default, in addition to providing the CHKDSK command. It detects physical file system errors and silently fixes them on the fly. Thus, many problems previously discovered on running CHKDSK never appear. It is administered by fsutil repair command.WEB, Chen, Ken, NTFS Self-Healing is An Overlooked but Useful Feature in Windows 7,weblink Next of Windows, 4 August 2014, WEB, Pawar, Amit, Self-healing NTFS in Windows Server 2008 and Windows Vista,weblink Amit Pawar - Infrastructure blog, Microsoft, 13 February 2008,

The alleged Windows 7 bug

Before the release of Windows 7, InfoWorld reported an alleged memory leak in CHKDSK; according to the report, the chkdsk /r command would cause the memory consumption to reach the maximum and the system to crash. Randall C. Kennedy of InfoWorld attributed the original report to "various Web sources" and said that in his tests, the memory consumption reached above 90%, although he did not experience a crash. Nevertheless, Kennedy took the memory consumption for a critical bug that would derail Windows 7's launch and chastised Microsoft.WEB, Kennedy, Randall C., Critical Windows 7 bug risks derailing product launch,weblink Infoworld, International Data Group, IDG, 19 February 2015, 5 August 2009, Tom Warren of Neowin dismissed Kennedy's assessment of the alleged leak's significance.WEB, Warren, Tom, Windows 7 RTM contains a rather nasty chkdsk bug,weblink Neowin, 19 February 2015, 5 August 2009, Steven Sinofsky of Microsoft also responded that Microsoft could not reproduce a crash either but that the massive memory consumption was by design, to improve performance, and not a leak. Ed Bott of ZDNet also reviewed the claim with his own tests and observed that no crash would occur. Noting that chkdsk /r, by design, does not work on the system drive while Windows is online, Bott concluded "it’s arguably a feature, not a bug, and the likelihood that you’ll ever crash a system this way is very, very small and completely avoidable."WEB, Bott, Ed, A killer Windows 7 bug? Sorry, no,weblink ZDNet, CBS Interactive, 5 August 2009,


The ReactOS implementation is based on a free clone developed by Mark Russinovich for Sysinternals in 1998weblink

See also



Further reading

  • BOOK, Wolverton, Van, MS-DOS Commands: Microsoft Quick Reference, 4th Revised edition, 1990, Microsoft Press, 978-1556152894,
  • BOOK, Kathy Ivens, Brian Proffit, 1993, OS/2 Inside & Out, Osborne McGraw-Hill, 978-0078818714,
  • BOOK, Æleen, Frisch, 2001, Windows 2000 Commands Pocket Reference, O'Reilly, 978-0-596-00148-3,

External links

{{Commons category|Screenshots of CHKDSK}} {{Windows commands}}

- content above as imported from Wikipedia
- "CHKDSK" does not exist on GetWiki (yet)
- time: 1:18pm EDT - Thu, Jun 20 2019
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M.R.M. Parrott