Figure 3-1 shows four main focus areas of a Universal Serial Bus (USB) system. These areas are the Client Software/USB Driver, Host Controller Driver (HCD), Host Controller (HC), and USB Device. The Client Software/USB Device and Host Controller Driver are implemented in software. The Host Controller and USB Device are implemented in hardware. OpenHCI specifies the interface between the Host Controller Driver and the Host Controller and the fundamental operation of each.

图3-1展示了通用串行总线（USB）系统的四个主要关注领域，分别是：客户端软件/USB驱动程序、主机控制器驱动程序（HCD）、主机控制器（HC）和USB设备。其中，客户端软件/USB设备和主机控制器驱动程序由软件实现，而主机控制器和USB设备则由硬件实现。OpenHCI规范定义了主机控制器驱动程序与主机控制器之间的接口以及各自的基本操作。

The Host Controller Driver and Host Controller work in tandem to transfer data between client software and a USB device. Data is translated from shared-memory data structures at the client software end to USB signal protocols at the USB device end, and vice-versa.

主机控制器驱动程序（HCD）与主机控制器（HC）协同工作，在客户端软件与USB设备之间传输数据。数据在客户端软件端的共享内存数据结构和USB设备端的USB信号协议之间进行相互转换。