After reading the "USB Mass Storage Class Bulk-Only Transport"
specification, I got a concept about the transmission protocol between
my desktop PC and some portable USB devices such as external HDD and
external DVD-RW. Despite this, I have no idea about how my desktop can
understand the content in the storage media of the mass storage
device. We know the file system is different between HDD and DVD-RW.
Moreover, the file system of a optical disc maybe one of ISO9660, UDF
or UDF bridge...etc. I think after the USB cable is attached, the
device firmware can tell desktop its manufactory information to let
desktop know it is a HDD, CD-RW or DVD-RW. But,  how does PC know what
kind of file system the device has?

Could anybody give me any hint or reference document?

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> desktop know it is a HDD, CD-RW or DVD-RW. But,  how does PC know what
> kind of file system the device has?

It reads the important sector locations from the disk and tries to recognize
the filesystem.

--
Maxim Shatskih, Windows DDK MVP
StorageCraft Corporation
maxim@storagecraft.com
http://www.storagecraft.com

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"Maxim S. Shatskih" <maxim@storagecraft.com> wrote in message news:<d4laco$2ulg$1@gavrilo.mt
u.ru>... 
>
> It reads the important sector locations from the disk and tries to recogni
ze
> the filesystem.

But, as my understanding, the "important sector" is different between
HDD and optical disc. For HDD, we can get file system parameters from
sector 0 but for disc, we might need sector 16 to recognize its file
system. Because PC only can use UFI commands(like SCSI commands) to
communicate with device, does PC know which sector it should request
after it knows what kind of peripheral the device is? I guess there
should be a scheme which defines what data PC should request at first.
However, I don't know how to find related articles efficiently by
Google yet.

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> communicate with device, does PC know which sector it should request
> after it knows what kind of peripheral the device is? I guess there

The OS kernel - be it Windows or UNIX - enumerates all filesystems and asks
each one to mount. If the FS returned OK - then all is done. If the FS retur
ned
error - then the next FS is tried.

UNIX also supports only trying a particular filesystem, Windows does not.

So, FSs execute the recognition sequence themselves, and are free to issue a
ny
reads they want. CDFS will read sector 16. UDF will read sectors 256, N and 
N -
256. FAT will read sector 0, and so on.

All of this is the issue of the OS kernel, not of the hardware. hardware can
only execute CDBs.

--
Maxim Shatskih, Windows DDK MVP
StorageCraft Corporation
maxim@storagecraft.com
http://www.storagecraft.com

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