USB mass storage device class (in English: USB mass storage device class, also known as USB MSC or UMS) is a protocol that allows a device with a USB interface to be connected to the main computing device to transfer files between them. For the main computing device, the USB device looks like a mobile hard disk, allowing drag and drop file transfer. In fact, it is a summary of many communication protocols adopted by the USB Implementer Forum, which provides interfaces for many devices. Including mobile hard disk, flash disk, mobile optical drive, card reader, digital camera, digital music player, PDA, mobile phone, etc.Universal Serial Bus (English: Universal Serial Bus, abbreviation: USB) is a serial port bus standard that connects computer systems with external devices. It is also a technical specification for I/O interfaces. It is widely used in personal computers, mobile devices and other information communication products, and has been extended to photographic equipment, digital TV (set-top box), game console and other related fields.When multimedia computers first came out, the transmission interfaces of external devices were different. For example, the printer could only be connected to LPT port, the modem could only be connected to RS232, and the mouse and keyboard could only be connected to PS/2. The complicated interface system, together with the limitation that the driver must be installed and restarted before use, will cause users' troubles. Therefore, it has become an inevitable trend to create a unified and easy to plug external transmission interface, and USB came into being.The latest generation of USB is USB 3.2, with transmission speed of 20Gbit/s, three-phase voltage of 5V/12V/20V, and maximum power supply of 100W. In addition, only a few USB Type-A, Micro-B and new USB Type-C connectors are no longer positive or negative.USB Developers Forum (English: USB Implementers Forum, abbreviation: USB-IF) is a non-profit organization that promotes and supports the universal serial bus. The main business is to promote and market the maintenance of USB, wireless USB, USB OTG and their related specifications and standards, and also develop and implement compatibility plans.The USB Developer Forum was established in 1995 by a group of USB developers. Famous members include Computer, HP, Enyixi, Microsoft, Intel and JEER Systems.The working committees in USB-IF are:Device Element Working GroupCompatibility CommitteeMarketing CommitteeOTG Working GroupThe USB-IF website provides developers with the ability to freely log in to the developer forum page and access files. However, they must first become registered members or employees of member companies to participate in the working group. The developer forum covers the development of USB software and hardware and is not a forum for end users