802.11b - This technology supports bandwidth up to 11MBps, which is comparable to the speeds of traditional Ethernets. 802.11b uses the same 2.4GHz radio
signaling as the original 802.11 standard. Because it is an unregulated frequency, 802.11b devices run the risk of incurring interference from appliances that use the same 2.4 GHz range, such as microwaves and cordless phones. However, if you install 802.11b devices out of range of other appliances, you can avoid the interference. Some manufacturers prefer using unregulated frequencies, such as 802.11b to lower their production costs. On the negative side, 802.11b is relatively slow and supports fewer simultaneous users.
802.11a (not recommended for most wireless users) - IEEE created 802.11a at the same time it made 802.11b. 802.11a supports bandwidth up to 54 Mbps and signals in a regulated 5 GHz range. This higher frequency limits the range of 802.11a in comparison to 802.11b, and due to its higher cost it’s used primarily in the business sector rather than in homes. 802.11a’s higher frequency also causes its signals to have difficulty penetrating walls and other obstructions. Because they utilize different frequencies, 802.11a and 802.11b devices are incompatible with each other.
802.11g - This technology supports of up to 125 Mbps, uses the 2.4 GHz frequency and is backwards compatible with 802.11b devices. 802.11g supports more simultaneous users, offers the best signal range and is not easily obstructed. The disadvantages of 802.11g is higher cost and possible interference with appliances on the unregulated signal frequency.