USB3.0协议规范(英文完整版).pdf

USB 3.0标准，使用USB3.0时从标准做起。 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 bi-directional, 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, mice, etc. 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