The most ubiquitous of input devices, keyboards tell the BIOS and ultimately the CPU which keystrokes you've entered. Keyboards use two methods to detect and report keystrokes: contact, or switch, and capacitive. Contact types are older, using a mechanical switch to close a circuit with each keystroke. Capacitive keyboards do away with the mechanical switch in favor of reliance on a change in capacitance (stored energy charges) to read the stroke. Contact keyboards come in several varieties, the most popular with spring-loaded keys, but also appearing with "rubber domes" and "membranes," both of which tend to survive longer in dusty, dirty environments. Your preference for audible and tactile feedback may determine your preferences here. Capacitance keyboards tend to last longer than contact keyboards, but cost a bit more. Also check out the new wireless keyboards.

Win ME, 2K, and XP owners have an "OnScreen Keyboard." This little goodie gives you a keyboard that appears on your screen and can be accessed through a mouse or other input/pointing device. To access the On-Screen Keyboard, from the Start menu select Programs, Accessories, Accessibility, On-Screen Keyboard. Then open the application that you wish to use with the On-Screen Keyboard. Select the keys on the On-Screen Keyboard to enter characters into the active application. Optionally, select Keyboard to choose the keyboard appearance and layout options as necessary. Optionally, select Settings, Typing Mode to adjust the typing method. Select the typing mode as appropriate for your needs. If you select hover mode, choose the hover time interval before characters are selected. Click the OK button. To close the OSK, just click the Close button. The idea is to make keyboard access easier for disabled users, but laptop and tablet PC users who dump coffee on their keyboards may find this a useful, if short-term, workaround.

Cleaning your keyboard is a necessity. Here's how. First, unplug your keyboard, hold it upside down over a sheet of newspaper, and tap it gently to remove loose crud. Next, take it outside and use a can of compressed air to blow out the dirt between the keys. Turn it over and tap out the loose crud again. Now, make a solution of dishwashing liquid and water, and use a dampened cloth to clean the key surfaces. Wipe dry. You can use the dusting attachment (the brush) on your vacuum cleaner to go over the keyboard one more time. Still dirty? Sometimes they get filthy, especially if you, like me, have teenagers who like to eat sloppy food with one hand and type with the other. Here's some tips strictly for filthy keyboards that use membrane-type keys (the mechanical keyboards have spring-loaded keys that make a distinctive clicking sound when they are pressed). Pop off the keys one by one -- you will probably want to use a digital camera or copy machine to make a copy of the key layout so you get the keys back on in their proper places. Remove the smaller keys with a small screwdriver, and be gentle. Don't remove the bigger keys such as Enter and the spacebar. Use compressed air and a damp cloth as above to remove the smutch. Really tough crud can be removed with cotton swabs dampened with isopropyl alcohol. Use the compressed air again. When everything is dry, replace the keys. Make sure everything works properly when you reattach the keyboard.

Actually, a mouse is just one type of pointer device used by various machines to input data. It's by far the most popular, first developed by the Xerox PARC team in the 1970s, introduced to the PC market by Apple for the Macintosh in 1984 (in the notorious one-button version) and carrying on strongly ever since. Different mice are used for different machines: Mac mice depend on a single button, Unix mice use three, and most PC mice use two buttons, with some manufacturers assigning custom functions to a third button and many sporting a central "wheel" for scrolling. Today's mice no longer use the serial port or a bus card to connect, preferring to connect either through a USB port or directly to the motherboard. Windows has a standard mouse driver program inbuilt to drive a mouse, but that generic driver is replaced by whatever driver comes with the mouse currently installed. That's why you can't just plug in an alien mouse and blast away; each mouse uses a specific driver, usually provided on a floppy or CD. Trackballs are very similar to mice, except they roll inside a socket instead of freely on a mouse pad. Trackballs are even more susceptible to dirt and gunk than a mouse, which can go down within hours in a dirty environment. Trackpoints and touch pads are other versions of pointing devices similar to trackballs, and are even less popular than the trackball. Mice are by far the preferred pointing device currently available. New on the market: wireless mice, which replaces wires with optical interfaces. Really new on the market: much smaller mice that are designed to work with laptop and notebook devices.

You can configure your mouse's functions by going through the Control Panel applet (in XP, the Mouse tab is under Printers and other hardware). Note: different mouse software gives users different options. You can control the speed of your mouse's sensitivity to double-clicking, or even set the mouse to open items with a single click. If you have something called "ClickLock," you can have the mouse click&drag by simply holding down the button for a moment or two, and release the dragged item with another click. You can control the rate and sensitivity of your mouse's scrolling; if you have a wheel mouse but you're missing the "Wheel" tab or its equivalent, you may need to download a newer driver from your mouse maker's Web site. Pressing the wheel on some mice may activate "panning" or a variant of the "AutoScroll" feature. You can adjust the speed at which your cursor moves in response to the mouse. You can also make your cursor instantly appear over the default option when you open a dialog box, though this option can make you hunt for your cursor over and over again. Win ME labels this option "Smart Move," while 2K and XP call it "Snap To" or "Snap To Default." You can have the cursor disappear when it isn't in use, or not. You can have the Ctrl key, or another key, locate the cursor with a visual effect when pressed. You can enable or disable pointer trails that display behind your mouse (especially good on small screens like notebooks). You can have the mouse controlled by the keyboard if you really hate using the mouse, by enabling an option called "MouseKeys." And of course, you can change the various cursors as you like -- if you really want to get fancy, there are plenty of animated cursors and fun things available on the Web to spice up your cursors.

How to use the mouse in old DOS games? Win 98 has a "Mouse_in_DOS" command that can be inserted into the SYS.INI file, but that doesn't help the rest of us. There are several ways to stroke this particular cat. Your system may include a MOUSE.EXE or MOUSE.COM file -- essentially an old mouse driver utility for DOS. Or, you can grab a mouse driver for free from most download sites online, including dos.li5.org/downloads/drv.htm. The more-or-less universal Microsoft mouse driver is here: downloads.zdnet.co.uk/downloads/detail/1002-2110-900552.html. Most other mouse vendors' sites also have brand-specific drivers, if you need them. Warning: a mouse connected to a mouse port -- or even an old serial mouse connected to a comm port -- will work fine in DOS with the right driver. But USB devices generally don't work in DOS, and that includes USB mice. Lots of sites offer how-to info on installing and using a mouse driver. This Gateway support site provides useful (and generally applicable) info: service.gateway.com/gateway/step/0,,5+26+35992+34554+25826+18566,00.html. XP users should take a look at the following sites: www.annoyances.org/exec/show/article07-114 and www.minnemacs.com/manyhighways/sandbox/xp.html.

Here's a good chunk of info on the optical mouse, adapted from Vince Underwood's piece on the subject in his November 2002 newsletter. Thanks, Vince!

Developed by Agilent Technologies and introduced to the world in late 1999, optical mouse sensor technology works by taking thousands of digital pictures per second with a resolution of up to 800count/in to determine the movement of the on-screen cursor. These individual images are then sent to the digital signal processor (DSP), which compares each picture with the last to detect movement. In doing so, the processor executes 18 million instructions per second. The mouse then outputs the signal to the computer via a USB or PS/2 port, and the software handles the rest of the work. What this translates to is a more accurate representation of the mouse's movements and a more accurate implementation of what the user wants to do with the mouse. Gamers will reap the benefits of these mice as they are very quick and accurate in their aiming ability. Optical mice avoid the need for a mouse pad and offer more precise pointing and movement than mechanical mice, as long as you don't put the mouse on a surface that reflects or shines. The mouse needs to report back to the processor with comparison images, so placing it on a reflective surface or even a glass surface will produce the exact same images when moved across this surface. And since optical mice have no ball or cavity, no cleaning is necessary, making them more reliable and longer lasting. They provide automatic power conservation during periods when the mouse is not moved, and controlled drive for the LED light source. Optical mice operate on a single power supply and feature on-chip LED drive and power conservation mode during times of no movement.

Touch screens, light pens, golf simulators, scanners, digital cameras, and microphones are only some of the other input devices out there. The idea is the same, though: to render the human output into a form the PC can understand.

The KVM switch is a new kind of device on the market that lets you switch back and forth from one computer to another while still using the same keyboard, video, and mouse input devices. You can use a KVM switch to alternate between laptop and desktop machines, between multiple desktops, or whatever, saving lots of cash and desktop space. Just remember that the KVM switch needs to support the highest video resolution of all the machines you intend to use, and that some KVM switches degrade images at high performance, so shop around and do your homework before buying.