Q: What is a hidden file?

A: Ever see a dog with one of those conical-shaped pieces of plastic around its neck? The vet puts those on to prevent the animal from reopening a wound with its teeth. We may think we are smarter than the typical pooch, but hidden files were designed to do the same thing--to prevent us users from hurting ourselves.

We may tell our friends that we run Windows 95 or Windows 98, but in reality we are running a very complicated house of cards that rests on an old operating system called DOS (disk operating system).

I know I am going to sound like a computer geezer by saying this, but personal computers originally ran with one floppy, then two, then a floppy and a hard disk. Many competing ways were designed to control how you got data into and out of these floppies and hard disks; the one that prevailed was DOS from Microsoft.

The way to control a computer in those days was with cryptic (the "pipe" instruction comes to mind) commands from the keyboard. These keystroke combinations were extremely powerful--you could easily erase all the files on the hard drive. Hidden files were designed so that a typical end user would not erase important files such as MSDOS.SYS and IO.SYS.

Q: How can you tell if your modem is going bad?

A: First of all, if you have a 56-Kbps modem, don't think there's something wrong if you're not getting data at that speed. Under Federal Communications Commission rules, the limit on transmission speed is 53 kilobits per second, and you're often connected with your Internet service provider at an even slower speed.

Still, if you test a lot below par, your modem could have been hit by a power surge.

One standard technician's trick is to swap out modems. Borrow a modem from a friend. If the replacement modem is also slow, then you must go down the checklist.

First call up your service provider and ask what chip set it uses on its modems. Today's standard is called V.90--it was preceded by competing standards called K56flex or X2. Get a modem that matches your ISP exactly.

Many readers have purchased internal modems called "winmodems." My experience is that they are not as rugged as good old external modems. Throw out the winmodem and get an external modem.

Winmodems depend on Windows code to run and are more sensitive to line conditions. One of these line conditions might be other appliances hooked up, such as a fax machine or one of those combination printer/fax bundles of headaches. Many people report that these devices draw power from the telephone line even when they are off!

Q: Why should I use Word when I have two other word processors, Notepad and Wordpad?

A: Here's a good way to remember the difference among the Microsoft products: Notepad is the fuzzy little lap dog, Wordpad is the Taco Bell Chihuahua, and Word is the big dog.

Windows 98 is set up so that if you click on any files that end in ".txt" they will be opened with Notepad; when someone knocks on the door, the lap dog will yip excitedly. When the lap dog sees a Jack Russell terrier, it hides under the couch; when Notepad gets a file larger than 57K, the system tells you to use Wordpad.

The Chihuahua (Wordpad) is also a small dog, but with a big-dog ego. Wordpad can handle older Word files (Word 6.0), can give you 16 colors and is so tough it can insert bullets.

But when you get complex documents (the big enchilada), you gotta call out the mastiff--Microsoft Word 97.

John Gilroy of Item Inc. is heard on WAMU-FM radio's "The Computer Guys" at 1 p.m. on the first Tuesday of the month. Send your questions to him in care of The Washington Post, 1150 15th St. NW, Washington, D.C. 20071 or via e-mail at jgilroy@iteminc.com.