A mass storage driver is a type of software designed to allow a computer to interact with an internal or remote storage device. Hard disk drives (HDDs), universal serial bus (USB) drives, external compact disc (CD) drives and every other type of mass storage device requires some type of driver to work. Operating systems (OSes) typically include the necessary software to interface with these devices, though certain products require proprietary drivers. The on board storage components of many different consumer electronics, such as cellular phones and portable music players, can also be accessed by using a mass storage driver. In this case, the computer will see the device as a remote hard drive once it has been connected.
Mass storage is a term used to describe any type of storage medium that can contain a large amount of data and also be written to and read by a computer. In the context of personal computers (PC), this can refer to anything from a multiple-terabyte hard drive to a USB stick that holds less than a gigabyte of data. Even floppy disk drives were referred to as mass storage devices, despite a limited storage capacity. Hard drives are the most common type of mass storage, though many different external and removable forms are also in common use. Each of these different storage mediums requires some type of mass storage driver to operate.
The primary function of a mass storage driver is to act as an intermediary between an operating system and a piece of hardware. When an operating system or another program sends a command to a mass storage device, it is really sending that command to the driver. The command is then translated by the driver into an instruction set that the mass storage device understands. Each operating system and device requires a separate driver, though there are some exceptions. In the case of storage devices, most units that fit into the mass storage class (MSC) can be operated by the same generic instruction set.
Many devices that are not primarily intended as remote storage can interface with a computer via a mass storage driver. This is what occurs when certain cellular phones, digital cameras and portable music players are plugged into personal computers. If the device is capable of accepting MSC instructions, the computer may be able to recognize it using a generic mass storage driver. This can allow files to be transferred to and from the device just as if it was a hard drive.