USB 1.0 and 1.1
These certifications refer to transfer rates at a speed of 1.5 Mbit/s (megabits per second) and 12 Mbit/s for USB 1.0 and 1.1 respectively. These can also be referred to as low speed and full speed (not to be confused with the much faster designation of hi-speed USB 2.0). These standards represent the lowest speed achievable by all devices including USB hubs. For most devices USB 1.0 and 1.1 are painfully slow, but this standard was replaced by hi-speed USB 2.0 back in 2001.
USB 2.0
As I referred to earlier, hi-speed USB 2.0 was introduced in 2001 and is capable of transferring at a rate of 480 Mbit/s. In theory, it can reach speeds at a whopping 60 MB/s (megabytes per second)! You will rarely see that speed achieved because while the connection can sustain 480 mbit/s, the devices themselves are not capable of fully utilizing the bandwidth. USB 2.0 is also fully backward compatible with the first generation USB. If the connection is hindered in some way (using an old hub or too long of an extension cable), the rate will default to full speed USB 1.0.
USB 3.0
USB 3.0 is not out in any devices yet, but it promises to be extremely fast. It is capable of transferring at a mind-blowing rate of 5 Gbit/s (gigabits per second)! It was developed and released by Intel in August of 2008 and also goes under the name of SuperSpeed. To be able to utilize USB 3.0, you will need a new motherboard and cables that supports the connection. Currently, there are no motherboards and devices available on the market with the connector, but they should appear within the next year.