USB devices report their attributes to the Host using descriptors. A descriptor is a data structure with a defined format. The Device descriptors represent the entire device, hence there is only one device descriptor per device. It specifies USB version, maximum packet size, Vendor, Product IDs, and the number of possible configurations. The Configuration descriptor provides what a USB device needs to have configured before its function may be used. The Host is responsible for configuring a USB device. Within a single configuration, a device may support multiple interfaces.