UMS | USB Mass Storage Device Class Explained

Written by John Harris, Updated on October 11, 2023


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.

usb mass storage device class

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 drag-and-drop file transfers. These protocols assist the host computing device to interface with a number of other storage devices.

How Does UMS Work?

UMS sets a standard communication protocol between USB storage devices and hosting devices such as computers and smartphones. UMS typically employs universally supported file systems like FAT32 and exFAT, which organize data on the storage device and allow the host to perform read and write operations.

Using a plug-and-play mechanism, the OS automatically detects the storage device. Once the device is detected, the host can access files on the USB drive, and users can read files from the USB device. After using the USB device, the user can safely eject it from the system to prevent data loss or corruption.

UMS Supported Devices

Devices that use this standard are called MSC (Master Storage Class) devices. Initially abbreviated as MSC, it's also commonly referred to as UMS (Universal Mass Storage).

UMS is supported on various devices including:

  • External magnetic hard drives
  • Digital cameras
  • USB drives
  • SSDs
  • Mobile phones
  • Card readers

UMS OS Support

Most common operating systems like Windows, macOS, Linux, and Unix-related systems like Solaris, NetBSD, FreeBSD, OpenBSD, Digital UNIX, and AIX have supported USB mass-storage devices from different versions and can work with USB storage devices. Older systems might need updates (patches) for this support.

Gaming Consoles like Xbox 360 and PlayStation 3 support most mass-storage devices for media transfer.

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