In the USB specification, which can be divided into 5 sections, namely, controllers, controllers, drivers, USB chipset drivers, USB devices, and for different client device driver for the device.
Controller (Host Controller): this is a physical chip, it is mainly responsible for the implementation of orders issued by the controller driver. Almost all current controller is integrated into the motherboard South Bridge chip, without requiring users to be purchased separately.
Controller driver (Host Controller Driver): establish a communications link between the USB controller.
USB chipset drivers (USB Chip Driver): provides support for USB.
USB devices (USB Device): with USB peripherals connected to the PC, including USB hubs and devices. The former to connect other USB devices, while the latter is used to accomplish a specific function of the device.
The client device driver (Client Driver): used to drive the USB drivers for the device, usually provided by the USB device manufacturer or operating system.