CHKDSK (CheckDisk) is a Microsoft disk utility that verifies the integrity of your file system and the hard disk drive blocks. The default mode scans the file system for logical errors but it will not fix any of the problems it finds. There are two user options that can be selected when running this program. One option tells the utility to fix all the problems it finds in the file system. The other option starts the utility to do an exhaustive check of the disk surface looking for any bad blocks. If any bad block is found, the utility will attempt to recover the data to a new block before it removes the bad one from use.

Do not wait until you start experiencing problems. Run CheckDisk once a month to see how your disk is doing. If you start seeing lots of bad sectors, consider getting a new disk.
Starting Check Disk

You can run CheckDisk under Windows XP or Vista using one of the following methods:

   1. In Explorer or My Computer, right click on the drive, select Properties, select the tools tab, and click on the Check Now button. Check both of the available options and click Start button. If you are checking your boot disk, you will be asked if you want to start CheckDisk when the system reboots. Click the Yes button and reboot your computer.

      Windows Hard Drive Utilities: chkdsk utility, defrag utility, backup utility

   2. Start a command window and type CHKDSK/? to get a listing of all the options. As an example, to check and repair errors on the C drive use this command:

          CHKDSK/F/R C:

Autochk.exe

For Win 2000, XP, or Vista, autochk.exe is the chkdsk program that gets run at boot time specifically for the boot hard drive. If you try to run chkdsk on the boot drive, your job will be scheduled to run when Windows boots because chkdsk cannot work when any files on the disk are open.

The 'dirty bit' on the file system is used to trigger autochk.exe at startup. While windows is running, you can check the status of the dirty bit by entering this fsutil command into the cmd window (start >> Run >> cmd.exe):

    fsutil dirty query C:

If autochk runs at boot time but you did not schedule it to do so, then some file system error event must have set the dirty bit. This should be a one time event because Autochk will clear the dirty bit when it completes successfully.

If autochk continues to run every time you boot your computer then you likely have a hardware problem. You can verify the problem by running a hard drive manufacturer's diagnostics on the drive. If there is any indication of a hard drive problem, consider yourself lucky that you can still read your data, and run out to buy that bigger hard drive you've been looking at.
Notes on the Command Line Version

Command line parameters:

    * /R - locate errors on the disk

    * /F - fix errors on the disk

In the command line version, if you just enter the command without any other parameters, you will get no useful results and the check disk utility may even look like it's stuck. So, at a minimum, use the '/R' flag to locate bad blocks.

Some command line versions require a space between the flags and the command:

    CHKDSK /F /R C:

Check Disk Utility History

The six character file name shows that this utility has its origins in the old MS-DOS world of eight character file names. The name is short for "CheckDisk." Its original function was to verify the consistency of the file system FAT pointers. Then along came the ScanDisk utility that incorporated the file system checking features of CheckDisk and added the ability to examine the hard disk for media defects. Now in Windows XP, the ScanDisk utility has gone away and its newer features have been incorporated back into CheckDisk.

Before MS-DOS 5.0, the program file was a com file: "chkdsk.com"; in MS-DOS 5.0 through the Windows systems, the program file is an exe file: "chkdsk.exe". To further complicate the naming nuances, when you go through the XP disk properties menu, CheckDisk is called "Error-Checking".
Hardware Considerations

CHKDSK is a high-level file system utility and so it is not concerned about various low-level details of your hard disk drive. It doesn't matter to chkdsk if your hard drive is a terabyte or 80 megabytes. It doesn't matter if the drive manufacturer is Seagate, Western Digital, Maxtor, Hitachi, or whoever. It doesn't care if your hard drive interface is Parallel IDE, SATA, SCSI, or USB. It doesn't care if your 'C: drive' is just a small partition on a larger hard disk.

The CHKDSK utility works on any drive that has been formatted with a Windows supported file system; this typically means either NTFS, FAT32, or one of the FAT32 predecessors.