USB mass storage device class (UMS) is also known as USB MSC. UMS is a set of computing protocols that enable the computer to recognize and interoperate with USB devices. These protocols are defined and developed by the USB Implementers Forum (USB-IF), which is a non-profit organization that is dedicated to the development and maintenance of USB standards.
UMS device class makes your USB device accessible to a host device and permits secure transfer of files between the host computer and the USB device. The USB device acts as an external hard drive to a host, and allows the drag-and-drop file transfers. These protocols assist the host computing device to interface with a number of other storage devices.
Devices that can be connected to the computers via this standard include External magnetic hard drives, optical drives, including CD and DVD reader and writer drives, solid state drives, digital cameras, digital audio and portable media players like iPod, flash memory devices, adapters between standard flash memory cards and USB connections, mobile phones, PDAs, and card readers etc.
UMS device protocol or standards are designed to be universal, that means with these protocols USB devices can be easily connected to computers with any OS. When a USB device is connected to a Macintosh computer, Mac will detect a USB device in the same way a PC computer will detect. Also, your USB device will work same with all computers, regardless of the operating system on the computer. Some of the supported OS includes: Windows, MS-DOS, Macintosh, Linux and other UNIX related systems.