Data cables work as differential pairs

Data cables work as differential pairs — the voltage pattern at their ends provides a stream of bits to the host controller. After plugging the device into the USB port, the controller picks up voltage changes on a data pin, which initiates a process called device enumeration. The peripheral is reset first to prevent it from being in an incorrect state, and then the controller reads all relevant information (such as device type and maximum data speed).

USB devices fall into one of many categories, each with a setup code — for example, a Bluetooth adapter falls into the wireless adapter category, while a force-feedback steering wheel falls into the physical interface device category.