802.11a

Despite the a designation for this extension to the 802.11 standard, 802.11a was available on the market after 802.11b. 802.11a differs from the other 802.11-based standards in significant ways. Foremost is that it operates in a different frequency range, 5 GHz. The 5-GHz range is much less crowded than the 2.4-GHz range, reducing the chance of interference from devices such as telephones and microwave ovens. 802.11a also offers considerably greater throughput than 802.11 and 802.11b, at speeds up to 54 Mbps. Range, however, suffers somewhat, and tops out at about 150 feet. Despite the superior speed of 802.11a, it never enjoyed the popularity of 802.11b.

Although you can get NICs and WAPs that support both 802.11b and 802.11a, the standards are not compatible with each other. A computer with an 802.11b NIC, for example, can't connect to a WAP that's only 802.11a, but could connect to an 802.11a/b WAP. Table below gives you the 802.11a summary.