USB, the abbreviation of universal serial bus, is an external bus standard, which is used to regulate the connection and communication between computers and external devices. It is an interface technology applied in PC field. The USB interface supports the plug and play and hot plug function of the device. USB was proposed by Intel, Compaq, IBM and Microsoft at the end of 1994. The next generation of USB interface will have a change direction. The next generation type-C USB interface can support both sides of the plug-in, and has strong data transmission signal. However, at present (2014) manufacturers are limited. As of December 26, 2015, many domestic manufacturers have used the data line based on the standard on their own mobile devices on a large scale.

Since the release of USB version 0.7 on November 11, 1994, USB version has experienced many years of development, and has developed to version 3.1, which has become the standard expansion interface in computers in the 21st century. Currently, USB 2.0 and USB3.0 interfaces are mainly used in the motherboard (2016), and the USB versions can be well compatible. USB uses a 4-pin (USB3.0 standard for 9-pin) plug as the standard plug. It can connect all peripherals in the form of daisy chain, which can connect up to 127 external devices without loss of bandwidth. USB needs the support of host hardware, operating system and peripherals to work. In the 21st century, the motherboard generally adopts the control chipset that supports USB function. The motherboard is also equipped with a USB interface socket. Besides the socket on the backplane, there is a USB pin reserved on the motherboard, which can be connected to the front of the chassis as the front USB interface for easy use (note: when wiring, carefully read the motherboard manual and connect according to the diagram, and do not connect it wrongly Damage the equipment). Moreover, the USB interface can also be connected by special USB cable, and more interfaces can be extended through hub. USB has the advantages of high transmission speed, easy to use, hot plug support, flexible connection and independent power supply. It can connect mouse, keyboard, printer, scanner, camera, charger, flash disk, MP3 machine, mobile phone, digital camera, mobile hard disk, external optical drive / soft drive, USB network card, ADSL modem, cable modem and so on.