Heirarchical Description

USB was designed having in mind devices with multiple capabilities. To infor the host of its multiple capabilities, a device describes itself hierarchically . A device may have multiple configurations, each of which may in turn have multiple interfaces, which in turn may have multiple endpoints. The interfaces also have classes (and sub-classes) associated with them. Common classes include those for human interface devices such as keyboard, mice etc. and those for storage devices such as hard disks. This allows a device to present the relevant interfaces/configurations for different purposes.