说明：  介绍 USB 的体系结构和特点包括总线特征协议定义 传输方式和电源管理等等这部分内容会使USB 开发者和用户对USB 有一 个整体的认识
(Introduced the USB architecture and features include the bus characteristics protocol defines the transmission mode and power management, and so this part makes USB developers and users an overall understanding of the USB)