usb 3.0標準下載：The original motivation for the Universal Serial Bus (USB) came from several considerations, two of the most important being:
• Ease-of-use
The lack of flexibility in reconfiguring the PC had been acknowledged as the Achilles’ heel to
its further deployment. The combination of user-friendly graphical interfaces and the hardware
and software mechanisms associated with new-generation bus architectures have made
computers less confrontational and easier to reconfigure. However, from the end user’s point
of view, the PC’s I/O interfaces, such as serial/parallel ports, keyboard/mouse/joystick
interfaces, etc., did not have the attributes of plug-and-play.
• Port Expansion
The addition of external peripherals continued to be constrained by port availability. The lack
of a bidirectional, low-cost, low-to-mid speed peripheral bus held back the creative
proliferation of peripherals such as storage devices, answering machines, scanners, PDA’s,
keyboards, and mice. Existing interconnects were optimized for one or two point products. As
each new function or capability was added to the PC, a new interface had been defined to
address this need.Initially, USB provided two speeds (12 Mb/s and 1.5 Mb/s) that peripherals could use. As PCs became increasingly powerful and able to process larger amounts of data, users needed to get more and more data into and out of their PCs. This led to the definition of the USB 2.0 specification in 2000 to provide a third transfer rate of 480 Mb/s while retaining backward compatibility. In 2005,with wireless technologies becoming more and more capable, Wireless USB was introduced to provide a new cable free capability to USB.