Sockets Universal Serial Bus (USB) are intended for connection to a computer of such external peripheral devices, as the mouse, the keyboard, a portable hard disk, the digital chamber, VoIP-phone (Skype) or the printer. Theoretically, it is possible to connect to one host-controller USB of about 127 devices. The maximal speed of transfer makes 12 Mbit/s for standard USB 1.1 and 480 Mbit/s for Hi-Speed USB 2.0. Sockets of standards USB 1.1 and Hi-Speed 2.0 are identical. Distinctions are covered in speed of transfer and a set of functions of host-controller USB of a computer, and USB-devices. USB provides a power supply for devices, therefore they can work from the interface without an additional power (if the USB-interface gives a necessary power, it is no more 500 mA on 5V). There are three basic types of USB connectors: USB A, USB B and mini USB.