Even if you think you know your ABGs, there's a lot more to picking a Wi-Fi adapter than just snapping up the cheapest 802.11b or g card. What makes a good card? Think broad compatibility, excellent reception and fool-proof drivers. Big names are no guarantee of quality, either -- some of the best adapters come from companies you've never heard of. And take those far-fetched range and throughput claims with two grains of salt. Real-world performance is what counts. Some cards deliver, and others don't.

So just how do Wi-Fi adapters differ? And why are some more equal than others? Here's how to separate the winners and losers:

Choose a Standard: A, B, or G

The first thing you need to decide is which type of card you need: 802.11b, 802.11a, 802.11g, or a combination: a/b or a/g. The original mass-market flavor of Wi-Fi was 802.11b, which first appeared in 1999. In mid-2001, 802.11a hit the market, offering faster speeds but no backwards compatibility, since it uses a different frequency band than 802.11b. Finally, in late 2002, 802.11g came along, offering both higher speeds and backwards compatibility with the large installed base of 802.11b equipment.

At only a nominal 11Mbps, with real-world data rates less than half that figure, 802.11b is obviously not meant for heavy-duty networking or streaming video. A few mostly discontinued 802.11b products purported to double the throughput to 22Mbps with proprietary solutions, but you needed to use the same manufacturer's card and access point to take advantage.

The 802.11a and 802.11g both offer a rated 54Mbps, nearly five times the original standard, although at different frequencies. 802.11a uses the 5GHz band, and because it has as many as 23 unique, nonoverlapping frequency channels, it's better at tasks such as streaming voice, video and multimedia than 802.11b or g. For now, 802.11a is popular mostly with consumer electronics vendors looking to network home entertainment systems, and with enterprises interested in voice applications. 802.11g uses the 2.4GHz band, the same as 802.11b, and is backward compatible with 802.11b, so that 802.11b cards can connect to 802.11g access points, and vice versa (although only at 802.11b data rates).

That backward compatibility has helped 802.11g to emerge as the new standard in both home and office equipment. Some vendors have taken it a step further, using Atheros chips that claim 108Mbps as their raw top speed. This faster, proprietary mode takes two Wi-Fi channels and "bonds" them together to achieve nearly double the throughput of one channel alone. The 108Mbps products are non-standard, and may or may not work across vendors in the high-speed mode.

Adding further variety to the mix, you can also get combination a/b and a/b/g cards with dual 2.4/5GHz radios. (All g cards are in fact b/g, because the g standard entirely includes b speeds.) The combination cards are useful when you need 802.11a for your work environment, for example, and 802.11b or g for your home network or at hotspots while traveling.

Check Your Chipsets

Probably the single biggest factor affecting compatibility and performance is the set of chips used in your card. Wi-Fi chips come from a long list of companies like Agere, Broadcom, Atheros, Texas Instruments, SyChip, and GlobeSpanVirata (formerly Intersil). Major vendors are often identified with one chip manufacturer or another. For example, the 108Mbps products from D-Link and NetGear use Atheros chips, while most current Linksys, Apple, Dell and Belkin products use Broadcom chips. Hence, several third-party cards based on the same Broadcom chips Apple uses work seamlessly with Apple's AirPort drivers, a major convenience. Likewise, NetGear and D-Link's 108Mbps products work together in high-speed mode.

The Wi-Fi brand means that any Wi-Fi-labeled adapters should be compatible with cards and access points from other vendors, no matter what chips they're using. And for the most part, they are. However, the Wi-Fi seal doesn't guarantee you won't get drops in performance when running a mixed b/g network (or even running a g network in the vicinity of another b network), and there are still the isolated and anecdotal cases of incompatibility. Many such issues are cleared up in firmware updates, however, so be sure to keep yours updated (both cards and routers) by regularly checking the manufacturer's Web site.

Power It Up

These days most major vendors highly customize their adapters with specialized antenna designs and optimized firmware. Some also have ports for attaching external antennas to improve reception even further. So even with the same chipset, there can be major differences in performance between cards.

Antenna design is critical to the performance you will get out of your card because it determines both signal transmission strength and receive sensitivity. Most standard cards only offer about 30mW of transmission strength when sending data, and a receive sensitivity of about -80dBm to ‑90dBm. By contrast, special high-powered 200mW cards with -90dBm to -96dBm of sensitivity offer huge increases in reception (a 3dB difference represents double the sensitivity). Cards with better sensitivity will let you get further away from the access point while still maintaining a usable signal. See FreeNetworks.org for more information about receive sensitivity differences among cards.

Take a Firm Stance

Software drivers and firmware also affect performance, although not to as great a degree as antenna design and the basic chipset itself. What's more important about good drivers and firmware is reliability, compatibility, and feature extensions (such as that oft-mentioned 108Mbps mode). If your company uses special Wi-Fi security features, for example, you'll need to be sure your card supports them.

Mac, Linux and PDA users will also want to be sure their platforms are supported. Third-party or freeware drivers are often available, but it's better if your card is explicitly supported for your operating system, so you can get technical help if needed.

Size Up Your Card

Wi-Fi adapters now come in all shapes and sizes, from the original PCI and PCMCIA card options, to USB, CompactFlash and Secure Digital (SD) card formats. There are even adapters that attach to regular Ethernet devices like printers and video game boxes and convert them to Wi-Fi. We'll get into all these in more detail on the next two pages, but suffice it to say that there's a card for everybody, whether you're at home, in the office, or on the road.

Don't Forget the Warranty!

Finally, factors like company strength and warranty support do matter. You'll want regular firmware updates for your card to accommodate new features (such as the addition of WPA encryption support), and good warranty and tech support policies when compatibility or installation problems occur.