MSD

The Mass Storage Device class (MSD) (also called Mass Storage Class (MSC)) is a USB class protocol which can be used to transfer files to and from storage devices.

As the USB mass storage device class is well standardized, every major operating system such as Microsoft Windows (after Windows 2000), Apple OS X, Linux and many more support it. So therefore an installation of a custom host USB driver is not necessary.

MSD allows sector-wise access to a storage medium. The storage medium can be a simple RAM-disk, NOR, NAND flash, SD card and so on. Sector-wise access means that the protocol itself does not necessarily know anything about the type of file system used or about any files or folder on the storage.

The protocol simple allows sectors to be read and written. This mechanic results in a light-weight protocol with very little overhead, but without knowing the underlying filesystem it can provide little in terms of file integrity. When a MSD stick is pulled from the host in the middle of a transaction it is possible for a file to end up half written which at best results in a corrupt file and at worst in a corrupt file system.