Media Transfer Protocol
|This article relies on references to primary sources. (February 2013)|
The Media Transfer Protocol is described by Microsoft, who introduced it, as a protocol for intelligent storage devices based on and compatible with Picture Transfer Protocol (PTP). Whereas PTP was designed for downloading photographs from digital cameras, Media Transfer Protocol allows the transfer of music files on digital audio players and media files on portable media players, as well as personal information on personal digital assistants. MTP is a key part of WMDRM10-PD, a digital rights management (DRM) service for the Windows Media platform.
Media Transfer Protocol (commonly referred to as MTP) is part of the "Windows Media" framework and thus closely related to Windows Media Player. Versions of the Microsoft Windows operating system from Windows XP SP2 support MTP. Windows XP requires Windows Media Player 10 or higher; later Windows versions have built-in support. Microsoft have also made available an MTP Porting Kit for older versions of Windows back to Windows 98. Apple Macintosh and Linux systems have software packages to support MTP.
The USB Implementers Forum device working group standardised MTP as a fully fledged Universal Serial Bus (USB) device class in May 2008. Since then MTP is an official extension to PTP and shares the same class code.
The protocol was originally implemented for use across USB but extended for use across TCP/IP and Bluetooth. Windows Vista supports MTP over TCP/IP. Windows 7 and Windows Vista with the Platform Update for Windows Vista also support MTP over Bluetooth. The host connecting to an MTP device is called an MTP Initiator whereas the device itself is an MTP Responder.
A main reason for using MTP rather than, for example, the USB mass-storage device class (MSC) is that the latter operates at the granularity of a mass storage device block (usually in practice, a FAT block), rather than at the logical file level. In other words, the USB mass storage class is designed to give a host computer undifferentiated access to bulk mass storage, such as compact flash, rather than to a file system, which might be safely shared with the target device (except for specific files which the host might be modifying/accessing). In practice, therefore, when a USB host computer has mounted an MSC partition, it assumes absolute control of the storage, which then may not be safely modified by the device without risk of data corruption until the host computer has severed the connection. Furthermore, because the host computer has full control over the connected storage device, there is a risk that the host computer may corrupt the file system, reformat it to a file system not supported by the USB device, or otherwise modify it in such a way that the USB device cannot completely understand it.
MTP and PTP specifically overcome this issue by making the unit of managed storage a local file rather than an entire (possibly very large) unit of mass storage at the block level. In this way, MTP works like a transactional file system - either the entire file is written/read or nothing. The storage media is not affected by failed transfers.
In case the device maintains a database/index of the content of the disk, MTP saves the cost of re-scanning the entire disk every time the content is modified.
Additionally, the MTP allows MTP Initiators to identify the specific capabilities of device(s) with respect to file formats and functionality. In particular, MTP Initiators may have to provide passwords and other information to unlock files, or otherwise enable digital rights management. Nothing specific of this nature is in the core standard but the features are available via vendor extensions. MTPZ, the Zune Extension to MTP specifically denies access to files until authentication has been processed, which is only possible using Windows Media Player 10 or higher.
By design, MTP devices (like PTP devices) are not treated as a traditional removable drive. The actual file system is implemented by the device, not by the computer's operating system. In theory the operating system may hide this difference, but this is not the case on Windows or Mac OS.[clarification needed] This also means that file system recovery tools on the computer will be of no use if the drive is corrupted, or crashes.
Large file transfers using MTP are much slower than with MSC. Also, once a file transfer selection has been started no other file transfers can be made. Having a file open can also prevent any transfers from being made.
The MTP and PTP standards do not support direct modification of objects. Modified objects must be copied out of the device and reuploaded in their entirety, which can take a long time for large objects.
MTP support 
On Microsoft Windows, MTP is supported in Windows XP if Windows Media Player 10 or later versions are installed. Windows Vista and later have MTP support built in. For older versions of Windows, specifically, Windows 2000, Windows 98 and Windows Me, Microsoft has released the MTP Porting Kit. which contains a MTP device driver. Some manufacturers, such as Creative Technology, also provide legacy MTP drivers for some of their players; these usually consist of MTP Porting Kit files with a customized INF file describing their specific players.
Most MTP-compatible devices are not assigned drive letters; instead, they appear as "devices" in applications such as Windows Explorer. Under Windows, MTP-compatible devices support a feature called AutoSync, which lets users configure Windows Media Player to automatically transfer all copied or newly acquired content to devices whenever they are connected. AutoSync is customizable so that the player will transfer only content that meets certain criteria (songs rated four stars or higher, for instance). Changes made to file properties (such as a user rating) on a device can be propagated back to the computer when the device is reconnected. Windows 7's sensor platform supports sensors built into MTP-compatible devices.
Copies of files accessed over MTP may remain on the host computer even after reboot, where they will be accessible to the user account which accessed them, as well as any other user accounts able to read that user account's files, including any administrative users.
There are several other Linux tools for accessing MTP devices in other desktop environments and from the commandline.
Other manufacturers 
Companies, including Creative Technology, Intel, iriver and Samsung, that manufacture devices based on Microsoft's "Portable Media Center specification", have widely adopted MTP. Supporting devices were introduced at the 2004 Consumer Electronics Show.
After an initial period of uncertain reactions, several large media player producers such as Creative Technology and iriver adopted the MTP protocol in place of their own protocols.
Many devices and audio software applications support MTP. Later versions of several operating systems, including AmigaOS, Android, AROS, Linux, Mac OS, and MorphOS, Symbian OS support MTP, sometimes with additional drivers or software.
See also 
- Media Transfer Protocol Implementation Details. MTP defined in slide 3
- Final Availability of Windows Media Player 10 Brings More Music and More Choices to Music Fans
- MTP, Portable Player Standard: Create Digital Music blog
- MTP Specification 1.0 on USB.org
- MTP Over Various Transports
- MTP Specification
- MTP Porting Kit
- Sensors and Windows - Windows Portable Devices Team Blog, MSDN 17 Dec 09
- Native gvfs backend for MTP devices
- git commit adding MTP backend to gvfs
- ArchLinux Wiki: MTP