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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 supports 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 standardized 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 restricted capabilities. Nothing specific of this nature is in the core standard but the possibility is allowed via Vendor extensions (whereas USB mass-storage does not cater for such 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. This also means that conventional file system recovery tools will be of no use if the drive is corrupted, or crashes.
As opposed to USB Mass Storage, a number of operating systems do not support MTP out of the box. Some even require third-party software.
Large file transfers using MTP are much slower than with MSC.
Neither the MTP nor the PTP standards allow for direct modification of objects. Instead, modified objects must be reuploaded in their entirety, which can take a long time for large objects. With PTP/MTP, the file size must be known at the opening stage.
On Microsoft Windows, MTP is supported in Windows XP if Windows Media Player 10 or later versions are installed. Windows Vista has MTP built-in. 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.
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 for these legacy Windows operating systems.
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.
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.