Microsoft said Monday that it isn't among those to fully back new wireless wunderkind 802.11a. The software giant hasn't issued an important Windows system certification for any modems that use just 802.11a, a new generation of wireless network, Microsoft said Monday. Wireless networks using 802.11a operate up to five times as fast as networks based on an older standard, 802.11b. There are between 15 million and 30 million 802.11b networks in homes and offices worldwide.

In avoiding the newer standard, Microsoft has repeated the same concern that has dogged the equipment based on 802.11a ever since the standard was approved in 1999: The 802.11a standard isn't compatible with 802.11b networks, which means an 802.11a modem card will not work with any wireless networks using 802.11b. To ensure compatibility with the older wireless networks, Microsoft is instead granting certification to equipment that uses both the 802.11a and 802.11b standards on one device, according to Microsoft. Such "dual mode" modems and access points are beginning to settle into the United States market after nearly two years in development.