Wireless adapters for the PCI interface, found in all PCs today, are much less plentiful than PC Card versions, and even less plentiful than USB adapters. The reason, once again, is that most desktops connect via Ethernet cable to an Ethernet adapter installed inside the PC.

But as wireless networking becomes more pervasive, particularly in homes and in offices converted from homes, these adapters, along with USB versions, are taking on a more substantial role.

Desktop PCs don’t seem to be going away as the prognosticators once insisted they would (price and expandability being two major factors), so they remain in heavy use, but people want to connect them to LANs and the Internet without stringing cables along the baseboard or finding a way to run them through the walls.

If you setup an access point and give each of your desktop PCs a PCI adapter, you can accomplish this quite readily. PCI adapters have one major disadvantage when compared with USB adapters.

Because of the way desktop PCs are constructed, anything installed in a PCI slot comes out of the back of the PC, precisely where you don’t want a wireless adapter to reside.

WLAN adapters need to communicate with other WLAN adapters (ad hoc) or with an access point (infrastructure), and the fewer physical obstacles between the wireless devices, the better.

PCs tend to sit on the floor, often against walls or with other furniture surrounding them, and the chances of blocking the signal to and from the other wireless components of your network is high. However, see Figure 1, which shows a PCI WLAN adapter featuring an external antenna to counter the line-of-sight issues.

For this reason, you should consider using PCI wireless adapters in only two situations:

• You have a clear “line-of-sight” from the back of your PC to the wireless adapter, and you have good reason to believe that the line-of-sight will remain uninterrupted in the future.

A clear line-of-sight means an unhindered area in which the radio signals can move between the two devices, with of course walls, ceilings, and floors part of the unchangeable components.

If your desktop PC sits on the floor, make sure you keep a few feet (at least) between its WLAN adapter and any walls, bookshelves, file cabinets, boxes, briefcases, and anything else that sits on the floor as well.

In other words, if you keep the PC in the open, you shouldn’t have too much trouble connecting. Unless, of course, the PC itself blocks the signal path, in which case you can simply turn it sideways.

• You don’t have any choice because your PC has PCI slots but no USB ports. If you have a PC purchased before roughly 2001, there’s a good chance of this, although it’s much less likely for PCs purchased in the past three years.

Still, PCs without USB ports do exist, and many companies and homes keep PCs for more years than PC manufacturers would like.

Of course, you can add USB adapter cards to an older PC, but if you add the cost of a USB adapter card to the cost of a USB wireless adapter, you’re probably above the cost of a PCI wireless adapter anyway.

Furthermore, if you’re using Windows 95, Windows 98, or Windows NT, you don’t have support for USB in your operating system. Windows 2000 support for USB is spotty at best, so if you use that OS, you’re also better off with a PCI wireless adapter.

PCI WLAN adapters present one other major inconvenience. To install them, you most open the computer case, and most PC users don’t like doing anything of the kind. Still, if this is your only choice, here are the steps to take.

1. Open the case. First, turn off the PC and remove the power cord from the case. If you can find the manual that came with your PC, it probably has the instructions you need for getting the case open.

If, like the vast majority of people, you tossed it into a pile or put it somewhere you were sure would mean something later on, and therefore have no hope whatsoever of locating it, opening the case is usually fairly easy (but not always).

Most cases have two side covers, held in place by screws or a thumb screw. After loosening the screws, slide the cover toward the rear of the computer until it detaches from the main structure of the case.

Other cases demand that you remove the front plastic panel of the computer, which you can do either by lifting from the bottom (you’ll find a kind of fingerhold at the base of the panel), or by prying the panel away from the main case using a screwdriver or butter knife.

Once the panel has been removed, slide the side cover, or more frequently the single-piece top and sides of the case, toward the front (which is why you have to remove the front panel) until you’ve freed it from the rest of the case.

2. Locate the PCI slots. With the PC case open, look inside. You should see the motherboard, a large rectangular circuit board with various cables attached (one to the power supply and others to your hard drives).

Figure 2 illustrates a typical motherboard layout, complete with its PCI slots (although yours aren’t all likely to be empty).

If you have a tower-style case (one in which the PC stands up rather than lying flat on your desk), lay it on its side so that the motherboard is parallel to the floor.

Along the side where the external cords attach to the PC (your monitor cable, Ethernet cable, the phone cords to your modem), you’ll find a row of long, narrow slots into which you can slide peripheral cards.

Today’s PCs typically have one AGP slot, usually occupied by the graphics card and five to eight PCI slots, many of which are also occupied. In fact, you might very well find only one PCI slot available for use.

3. Insert the WLAN adapter card. Without forcing it, but using enough elbow grease to get the job done, push the PCI WLAN card into a vacant PCI slot. If necessary, rock it into place until it fits snugly into the slot.

You know it’s right when the small metal lip at the top of the card sits flush with the inside ridge of the case. Match up the slot on the metal lip with the screw-hole on the ridge and screw the card into place, or anchor it in place with whatever other mechanism your particular PC uses.

4. Power on and install drivers. Close the PC by reattaching the sides or the single-piece top/side component of the case along with the front panel. Replace the screws or set the thumbscrews.

Attach any cables that came loose during your installation adventure and plug the power cord into the case. Power on the PC, wait for Windows to ask for a driver, and insert the CD that came with the PCI WLAN card.

Windows typically locates the driver on the CD automatically and installs the necessary driver, but if it does not, you’ll have to do so manually by using the directions found in the WLAN card’s manual or quick-start card. If you can find neither, look for a Setup.exe file on the CD.