a laptop USB port USB The USB bus is also said to \Hot pluggable\, that is to say that you can connect and disconnect a USB with the PC on. The system installed on the PC (Windows, linux...) recognizes it immediately. The USB has a very interesting feature : it's the mode standby when not using the device. Also known as \Power conservation\ : Indeed the USB bus gets suspended after 3 ms if it is no longer used. During this mode, the component consumes 500µA. Finally, the last highlight for USB is that this standard allows to feed the device directly with the PC so no power outside.