CHKDSK

In computing, CHKDSK (short for "check disk") is a system tool and command in DOS, Digital Research FlexOS, IBM/Toshiba 4690 OS, IBM OS/2, Microsoft Windows and related operating systems. It verifies the integrity of a volume and attempts to fix 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. An early implementation of a 'CheckDisk' was the CHECKDSK that was a part of Digital Equipment Corporation hardware's diagnostics, running on early 1970s TENEX and TOPS-20. The CHKDSK command was first implemented in 1980 by Tim Paterson and included in Seattle Computer Products 86-DOS. The command is available in MS-DOS versions 1 and later. CHKDSK is implemented as an external command. MS-DOS versions 2.x - 4.x use chkdsk.com as the executable file. MS-DOS versions 5.x and later use chkdsk.exe as the executable file. CHKDSK can also show the memory usage, this was used before the command MEM.EXE was introduced in MS-DOS 4.0 to show the memory usage. In DR DOS the parameter /A limited the output to only show the memory usage. CHKDSK and UNDELETE in MS-DOS 5.0 have a bug which can corrupt data: If the 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. CHKDSK can be run from DOS prompt, Windows Explorer, Windows Command Prompt, Windows PowerShell or Recovery Console. 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.