I am reprinting a post from the Xdev forums on why Google is using Media Transport Protocol (MTP) based storage instead of USB storage on Honeycomb (Android 3.0). This of course also pertains to the Xoom, which recently went on sale as the first Android 3.0 based tablet.
Forum user Gogol posed these questions:
“-What is the breakdown of that 32GB Xoom internal memory (how many parition (sp), how much space for apps / files)?
– Why Google is using MTP instead of USB file transfer on Honeycomb?”
He received the following response from a Google developer:
“MTP is a big improvement over USB mass storage — for devices with lots of internal memory, a manufacturer no longer needs to come up with some hard partition between the USB mass storage and internal storage. Instead, they are all in one partition, with MTP providing access to the directory of media files that would normally be available through USB mass storage. This means there is no longer a need for apps on SD card for such devices, because what used to be the ‘internal SD card’ is in the same partition as where applications are stored. The storage on your device can be used for either applications or media, depending on what you want to put on it. You aren’t stuck with how much space the manufacturer decided to leave for the two areas.
Oh also this means that the media storage doesn’t need to be unmounted from Android when it is being access through the PC.“
So now we know why: simplification, as well as untying the OS partition from user storage partitions, which is more convienient and more flexible.
A snippet also from Wiki about MTP:
“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.“
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Update – 21 August 2011: For those interested in how to use MTP on their desktop (Mac & PC) to transfer files to their Android tablet consult this post.