the development of USB From the first release of USB 1.0 RRC candidate standard began in November 1995, it completely solved the old inefficient interface problem. Although the original USB speed is not fast, it is simple and convenient, especially it can plug instantly and play instantly. However, with the advancement of technology, USB speed has also been increased by leaps and bounds, and the latest USB 3.1 has reached 10Gbps. The limitation of former USB interface also has been showing up: the plug must be plugged correctly, the data rate is not always as what you want ( such as many HD video now), and when USB is used for larger batteries ( these days many smartphones and tablet PC are using batteries of larger capacity) to have power supply, the batteries is in slow charging which is disappointing. （I was trying to write a composition about USB....）