`Lost Clusters': Serious Matter?

Q. I keep getting a message from one of my programs telling me that I've got "lost clusters" on my hard drive. What are they, are they bad and, if so, how do I get rid of them? B. Austin, Bellevue.

A. When you save data on your PC's hard drive, DOS (Disk Operating System) stores it in "clusters," also sometimes called "allocation units." Depending on how your hard drive is configured, an individual cluster may contain anywhere from 512 to 8,096 bytes of data.

That's not actually much data. In fact, this short column occupies about 12,000 bytes on my hard drive. Which means, of course, that most files on your computer are stored in multiple clusters.

DOS keeps track of what files are in what clusters with a File Allocation Table, which is essentially a map of all the clusters on the drive. This logical map identifies which clusters contain data for which files. Then, when you call up a file from within, say, your word processor, the computer checks the FAT to find just which clusters contain the data for that file and gathers them together.

All this is invisible to the user, who doesn't know - and probably doesn't care - that what seemed like a single file was actually saved in a bunch of separate pieces scattered across different parts of the hard drive.

Unfortunately, on those rare occasions when your system crashes or a program freezes up, either the File Allocation Table or the file entries it tracks may become damaged. And if the file entries on your drive don't match what is mapped in the File Allocation Table, you can't access the data in those clusters. In short, when a program tells you that it has found lost clusters on the drive, it is telling you that there are clusters containing data on the drive that, according to the FAT, shouldn't have any data in them.

There are two reasons you'll want to get rid of those lost clusters. First, they're taking up hard disk space. Second, they may have data in them that you want but can't access.

To get rid of the lost clusters, get out of Windows or whatever other program you might be running and return to the DOS prompt. Type cddos to move to your DOS directory. Then, if you're running "MS-DOS," version 6.2, type scandisk and follow the on-screen directions. ScanDisk will find and free up the lost clusters so that they can hold data again. If you're running an earlier version of DOS, type chkdsk to confirm that there are lost clusters on the drive. Then, if there are, type chkdsk /f to remove the lost clusters.

If you think the lost clusters may contain data you want, you can save the data to files by following on-screen prompts with either Chkdsk or ScanDisk. Then you can load the files in a text editor and see if any useful data actually survived.

Q. In a recent Q&A column you wrote that before opening the computer up "make certain you've unplugged the power cord." WRONG! You turn the power switch off, but leave the cord plugged in because the ground wire in the cord keeps everything grounded properly, reducing the chances that static will toast your system. Also, you shouldn't use an eraser to clean the contacts! This removes metal and any antioxidant coatings on the contacts, increasing the certainty of future oxidation problems. Use a contact cleaning spray available at any electronics shop. Will Kempf

A. Actually, most manufacturers advise that you should completely unplug the computer, and my experience reflects the wisdom of their advice. On a number of occasions, while working inside a computer, I've accidentally turned the unit on by hitting the power switch with my knee. As I noted in the column, before working on the computer you should touch grounded metal to disperse any static electricity.

As for the contact cleaner, you are, of course, correct. Using an eraser repeatedly on contacts could eventually cause problems itself, and if you really want to play it safe - particularly if you're frequently removing and installing add-in boards - you should buy some contact cleaner spray. But if your computer isn't working and you don't have any spray handy, I wouldn't wait through the weekend to buy spray before cleaning the contacts. Devil-may-care risk-taker that I am, I generally use an eraser and I've never experienced any problems as a result.

Q. Why do prices for the same computers vary so much? Is there any reason I should worry about buying from a discount mail-order service? R. Kipling, Seattle

A. A rose is a rose, and a 486 is a 486. No, not really. When you buy a computer from a vendor, unless you ask specific questions you can't be sure about the quality of the hard drive, the floppy drives, the video card, the power supply and other components. Discount vendors often put lower-cost components into systems. Sometimes, but not always, these lower-cost components are also lower-quality components.

But where discount vendors save the most dollars is in service. With a mail-order firm you can't stroll in and ask questions, nor can you try out equipment before you buy it. And you also may have more difficulty getting service if the equipment you buy goes bad. Some mail-order companies require you to ship your unit back for servicing at your own expense. Others back up the systems they sell with on-site service warranties, which means that if something goes wrong the company will send someone out to fix it.

Finally, know that while most mail-order computer firms are perfectly reliable, many buyers have experienced problems with fly-by-night mail-order companies billing charges to their credit card far in advance of shipping the goods. And some less-reputable firms have also failed to issue promised credits when goods are returned. Your best protection against such dealers is to check with the Better Business Bureau. You can also check computer magazines from a couple of years ago for the company's ads, just to make sure you're dealing with a firm that's been in business for a while.

Q&A by Patrick Marshall appears Sundays in the Personal Technology section of The Seattle Times. Marshall, a computer consultant on Mercer Island, is a contributing editor to InfoWorld magazine. Questions can be sent three ways: by e-mail at ptech@seatimes.com; by voice mail at 464-8452; and by postal mail at Q&A/Technology, The Seattle Times, P.O. Box 70, Seattle, WA 98111.