USB- is the abbreviation of English UniversalSerialBUS (Universal Serial Bus), and its Chinese abbreviation is "tong serial line"; it supports plug-and-play and hot-swappable functions of the device. USB was jointly proposed and formulated by Intel, NEC, Compaq, DEC, IBM (, Microsoft, NorthernTelecom, etc.) in 1994. The USBV0.7 version was published on November 11, 1994, and it has now been developed to version 3.1. 。USB has the advantages of fast transmission speed, convenient use, support for hot plugging, flexible connection, independent power supply, etc.; and USB certification is also called USB-IF certification, which is a voluntary iconic promoted by USB Implementers Forum (USB-IF) Certification.

1. Connector

USB2.0 standard types: USB Type A male, Type A female; USB Type B male, Type B female; Mini USB male, female; Micro USB male, female;

USB3.0 standard type: USB type A male, type A female; USB type B male, type B female; Micro USB male, female;

USB3.1 standard type: Type C male, Type C female;

2. Cable

USB2.0 standard type: USB A to B, USB to MiniB, USB A to MicroB

USB3.0 standard type: USB A to A, USB to B, USB A to MicroB

USB3.1 standard type: Type C to Type C

Certification tests for USB peripherals can be divided into three categories. The first is the electrical characteristic test, which verifies the signal quality of the product under different application architectures. Next is the functional test, which is used to check higher-level product details, such as the degree of support for standard requirements and device enumeration functions. The latter is the product interoperability test, which is used to determine the interaction between the tested product and other USB devices.