Chkdsk is a tool provided with Microsoft Windows 2000 and Microsoft Windows XP that is used to test and repair the computer's file system. The analogous tool for Windows 95/98/ME is called Scandisk.

This is a very important and often overlooked tool, which all users should use periodically to make sure there are no errors in their file system and to correct those errors that do appear.

Windows will run chkdsk, but only when errors in the file system have reached the point where Windows itself notices that there is a problem. In fact, problems usually have been present and propagating in the file system for awhile before Windows notices them. These problems are often responsible for subtle performance issues or strange malfunctions of your software. In fact, it has been our experience at Just So Software that the vast majority of support requests regarding our Property Management Software package are resolved by having the user run chkdsk.

You should run chkdsk whenever there is an anomaly - whenever your software does something unexpected, whenever you experience a "blue screen of death", prior to installing any package, after installing any package, after a power failure, both before and after an upgrade, and - if none of those things applies - once a week anyway. Most of the time, chkdsk will report no errors. But sometimes it will, and the times it does report and fix an error more than make up for the effort you took on the times that it did not find an error.

File system errors are a fact of life that comes about because of the huge complexity of these computers, and the very high density of storage on hard drives. It is not a problem that is exclusive to Windows file systems, but Windows is one of the worst about automatically checking and cleaning the file system, which is why you have to do it.

So, here is how you run chkdsk:

1. Go to Start->Run.
2. In the Run requester, type Cmd (without the quotes).
3. A command line window will open. In that window, type chkdsk c: (without the quotes).
4. The system will run chkdsk. Read the output carefully.
5. If chkdsk did not give any error messages you are done. If it finds errors it will tell you it is fixing them, but itreally is not. Dont believe it.
6. If chkdsk reported any errors at all, then type inchkdsk c: /f (without the quotes).
7. chkdsk will tell you that it cannot run and ask if a disk check should be scheduled for the next time the system restarts. You tell it yes.
8. Reboot.

There is a bug in the Windows XP version of chkdsk. Chkdsk may report an error that "security descriptors have changed" then will give an error message of "CHKDSK discovered free space marked as allocated in the master file table (MFT) bitmap". If you receive these two error messages together, this is normal system behavior that merely reflects that the system is running while chkdsk is running. In this case, ignore it. If the "free space marked as allocated" error appears WITHOUT the security descriptor error, then you should treat this as a valid error and run chkdsk to repair the file system. This bug in chkdsk is NOT present in Windows 2000; any reported errors there should be considered valid.

Periodically running chkdsk is the single most important thing you can do to ensure that your data stays safe and your computer continues to run without issue. Do not fail to do this!

Jim Locker holds advanced degrees in physics, has designed and developed computer systems and software for over 30 years, and was a landlord for 20 years running up to a couple of hundred properties. He presently works as an independent computer systems consultant and works for Just So Software, Inc. which produces one of the industry's premier property management software packages.

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