USB, the abbreviation of Universal Serial Bus (Universal Serial Bus), is an external bus standard used to regulate the connection and communication between computers and external devices. It is an interface technology used in the PC field.

Since its introduction, universal serial bus (USB) has successfully replaced serial ports and parallel ports, becoming one of the standard expansion interfaces and essential interfaces for a large number of computers and smart devices in the 21st century, and has now developed to USB 4.0 version.

USB has the advantages of fast transmission speed, easy use, hot swap support, flexible connection, independent power supply, etc. It can be connected to a variety of peripherals such as keyboards, mice, and mass storage devices. The interface is also widely used in smart phones. The interaction between intelligent devices such as computers and external data is mainly based on network and USB interface.

USB uses four-wire cables, two of which are serial channels used to transmit data, and the other two provide power to Downstream devices, and for any peripheral that has been successfully connected and mutually recognized, data will be transmitted at the highest rate that both devices can support. The USB bus will automatically dynamically convert from high speed to low speed in the compatible transmission mode according to the peripheral situation and match the lock at the appropriate rate.

USB as a token-based bus. Similar to token ring network or FDDI token-based bus. The USB host controller broadcasts the token, the device on the bus detects whether the address in the token matches itself, and responds by receiving or sending data to the host. USB manages USB bus power by supporting suspension/recovery operations.