USB 2.0 Versus 3.0
It is no surprise that current 802.11ac adapters utilize USB 3.0. The USB 2.0 standard, so called “Hi Speed,” theoretically maxes out at 480 Mb/s (60 MB/s), and USB 3.0 standard, also known as “Super Speed,” increases that to 5 Gb/s (625 MB/s). Of course, real-world throughput is usually quite a bit lower.
With 802.11ac's peak data rates exceeding what USB 2.0 is capable of over the 2.4GHz and, even more dramatically, the 5GHz frequencies, the use of USB 3.0 becomes mandatory for the necessary throughput.