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?