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. Where 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. Comparison with USB Mass Storage MTP's advantages are marked with "(+)" while disadvantages are marked with "(-)". File oriented instead of block oriented protocol By not exposing the filesystem and metadata index, the integrity of these is in full control of the device. (+) No risk of file system corruption if unplugging the device while writing. File transfers are atomic, meaning completed in a single operation, and no explicit file system unmounting ("safe removal") is required by the user, since the file system remains managed by the mobile device's operating system, and a mobile device is battery-powered, meaning power to the flash memory is not cut out