The 802.11a standard uses the same core protocol as the original [IEEE 802.11 (wireless networking)] standard, operates in [the] 5 GHz band, and uses a 52-subcarrier orthogonal frequency-division multiplexing (OFDM) with a maximum raw data rate of 54 Mbit/s, which yields realistic net achievable throughput in the mid-20 Mbit/s. The data rate is reduced to 48, 36, 24, 18, 12, 9 then 6 Mbit/s if required. 802.11a originally had 12/13 non-overlapping channels, 12 that can be used indoor and 4/5 of the 12 that can be used in outdoor point to point configurations.

source - IEEE 802.11a-1999. (2008, June 25). In Wikipedia, The Free Encyclopedia. Retrieved June 26, 2008, from http://en.wikipedia.org/wiki/802.11a

While 802.11a enjoyed a brief period as top dog in the wireless networking arena, the inherent difficulty in getting wireless signal at 5GHz to pass through solid objects typically makes it a secondary or tertiary choice for hotspot venues. That said, Hautspot does indeed sometimes utilize hardware employing 802.11a technology, typically for line of sight, point-to-point distribution systems. In addition, many new notebooks have built-in 802.11a/b/g hardware, making 802.11a once again available to the general public.