USB 2.0 was released in April 2000, adding a higher maximum signaling rate of 480 Mbit/s called High Speed, in addition to the USB 1.x Full Speed signaling rate of 12 Mbit/s. Due to bus access constraints, the effective throughput of the High Speed signaling rate is limited to 35 MB/s or 280 Mbit/s.
The goal of the new serial bus is to broaden the range of external peripherals that can be used on a computer. A hard drive can easily hit the USB 1.1 bottleneck whereas it now becomes more ‘usable’ under USB 2.0 conditions. For those people who found us via search engines, USB 2.0 should neither be called ‘USB2′ nor ‘USB 2′.
Further modifications to the USB specification have been made via Engineering Change Notices(ECN). The most important of these ECNs are included into the USB 2.0 specification package available from USB.