Be warned: ScanDisk has no Undo feature. Once it makes a change, that change is there to stay.

If you constantly have problems with ScanDisk not completing its run, try rebooting Windows in Safe mode and running ScanDisk from there (restart Windows, then press F8 when you see the words "Starting Windows 95" appear; with Win 98/ME, restart Windows and immediately press and hold the Ctrl key until the Startup menu appears). Chances are good that whatever program is interfering with ScanDisk won't load under Safe mode. Note: switching into Safe Mode from XP is a bit different: XP users need to enter MSCONFIG in the Start menu's Run dialog, then click on the BOOT.INI tab and check the /SAFEBOOT box. Reboot to enter Safe mode. Repeat the process and uncheck the box when you're through with Safe Mode. One caveat: Don't experiment with the other settings on this tab. You could wind up unable to get back into MSConfig to undo your changes.

If ScanDisk finds a number of cross-linked files, you've got problems. Before letting ScanDisk try to repair the problem, make sure you back up your files. Otherwise you'll lose something.

If ScanDisk finds a few lost clusters or file fragments, you're usually safe in letting the program wipe them out. If you're unsure, have ScanDisk save them to a file and use a word processor (not NotePad) to look these files over. If it finds lots of lost clusters or file fragments, chances are it has rearranged your file structure in a way you won't like. If you have a number of "Dir00001," "Dir00002," etc, or "File0001," "File0002," etc, you've got problems. Those directories and files were the result of ScanDisk's ham-handed attempt to fix major problems on your drive. It's doubtful that you can properly restore the original file structure.

If ScanDisk finds unstable sectors on your hard drive, that drive's days are numbered. Buy a new hard drive and transfer everything to the new disk.

Do a quick scan every day. Once every two weeks or so, do a more thorough full scan of all drive partitions. You can't scan too much.

ScanDisk is not a cure-all; it can only repair minor problems. The last time my computer crashed, ScanDisk repaired things enough to let me reaccess Windows (I ran ScanDisk from the C: prompt), but it didn't fix anything. It did let me get to my programs and back up critical files, though.

If your PC crashes while the printer is running, errant data from the printer data spool can quickly jam your hard disk with electronic gobbledy-gook. Expect Scandisk to remove a great deal of gunk in .CHK files.

Speaking of .CHK files, sometimes Scandisk yanks entire files and renames them with the .CHK extension. Here's two ways to (sometimes) identify and restore these mysterious files. The easiest way is if you already know what the file might be: for example, Scandisk does its thing, you come up missing a .GIF file, and you have a .CHK file that looks to be about the same file size. The file is probably named FILE0000.CHK; rename it FILE0000.GIF and try to open it with your usual graphics viewer. If it opens, fine. If not, delete it. The second way comes into play when you're not sure what the .CHK file might be. Open the mystery file in WordPad and note the first few characters of the file. They might identify the file type: BM indicates a .BMP file; GIF, a .GIF file, JFIF, a .JPG or .JPEG file; MZ, a program; PK, a .ZIP file. Don't save the file in WordPad! Rename it using the proper extension and try to open it using the proper application. If it opens, great. If not, delete it.

You can save yourself time and effort by automating your ScanDisk usage, by adding a few command-line switches to the appropriate Shortcut. After this, you can simply click the button and watch ScanDisk do its thing. To do so, right-click the Start button and choose Open or Explore. Locate the ScanDisk Shortcut, which lives in your Windows/Start Menu/Programs/Accessories/System Tools folder. (To make a shortcut for your desktop, right-click the ScanDisk icon, drag it to the desktop, and choose either Copy Here or Create Shortcut(s) Here.) Press Alt+Enter to open the Properties screen, click the Shortcut tab, then click at the end of the command line in the Target box. Then add the appropriate command switches (separated by spaces) to make ScanDisk perform as you like. Switches are as follows: For scanning a particular drive, type its letter followed by a colon (A:, C:,. etc.). For scanning all (non-networked) drives, don't type any drive letters, just type /a. For ScanDisk to start and stop without your input, type /n. Using this switch will not stop ScanDisk from stopping to report errors; if you don't want the error information, start ScanDisk and check Automatically Fix Errors. Let ScanDisk run to get this choice set. To make ScanDisk run in Preview mode - find the errors but not fixing them - use /p. Warning: Preview can mislead you into thinking that the errors have been fixed when in fact they have not. Your command line might look something like this: C:\WINDOWS\SCANDSKW.EXE C: D: /N , to make ScanDisk scan drives C: and D: and automatically exit when finished.

ScanDisk is a slow and not-so-thorough 16-bit program. Many experts recommend letting ScanDisk alone and instead purchasing Norton Utilities or McAfee's (formerly Helix's) Nuts&Bolts and using their more sophisticated scanning/repairing utility. However, ScanDisk won't create problems for you, while these programs sometimes will. My suggestion: try them out after performing a complete backup, be ready to uninstall them, and save your receipts.

Win95 OSR2, along with Win 98/ME, has the annoying feature of automatically running Scandisk after every "nonstandard" shutdown (i.e. when a program crashes or you "warm-boot" the system). You may not want this to happen. If not, you'll have to edit MSDOS.SYS to stop it from "autoscanning." Go through Windows Explorer and turn off MSDOS.SYS's hidden, read-only, and system attributes (explained elsewhere on this page). Open Notepad or another text editor and open MSDOS.SYS. Search for the [OPTIONS] section and add the line AUTOSCAN=0. Save the file, reset the attributes, and reboot your computer. Your Autoscan default setting is 1, which checks for a bit in the boot drive's Master Boot Record, which is reset every time Windows shuts down normally. A "nonstandard" shutdown does not reset the bit, which causes Scandisk to trigger upon the next bootup of the system. If you want Scandisk to run every time you boot up, change the line to read AUTOSCAN=2. Or, do it the easy way: download TweakUI from Microsoft's PowerToys site at www.microsoft.com/Windows95/downloads/contents/
WUToys/W95PwrToysSet and let it do the dirty work (access it through Control Panel and use the Boot tab). This is useful for the truly paranoid among us, or if your hard drive is showing signs of going belly-up. Remember, an unusual shutdown often means trouble, which means that running Scandisk is a good idea. Win 98 users, you should have a version of TweakUI on your Windows CD -- look for the TWEAKUI.INF file. It probably isn't the most recent version, though.

Infrequently, ScanDisk refuses to shut down, denying access to the computer. This is even more annoying when ScanDisk automatically fires up after an unusual shutdown and denies you access altogether, even to Safe Mode, without shutting down ScanDisk before it completes its duties. Again, TweakUI is the answer. Crank up TweakUI, go through the Boot tab, check the box that says "Function keys available," and restart your computer. Press F8 when you get the "Windows is starting" message and choose Safe Mode. If this still doesn't work, you'll need to go back into TweakUI and check the "Always show boot menu" box. You can uncheck this later. Now restart your computer; you can run both ScanDisk and Defrag in Safe Mode.

Want to make a Desktop shortcut to ScanDisk? Just drag&drop the Start Menu shortcut to the Desktop and select the "Copy Here" option.

Win XP users, Microsoft jettisoned the venerable ScanDisk for you guys. You can either use CHKDSK, which is even older, or use Microsoft's Error Checking feature. Access this feature by doing the following: In Windows Explorer, right-click the drive you want to check, and select Properties from the context menu. Now select the Tools tab. Under Error Checking, click "Check Now." If you want the scan to check the disk sectors or attempt to make repairs, select those options and click Start. Close Windows Explorer when you're done.