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USB mass storage devices - file system question


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Regarding USB-attached mass storage devices such as memory sticks, external hard drives, external device with their own internal storage, etc:

Does an Operating System (Windows 9X, 2K/XP, etc) interact with these devices such that it sees them *exactly* as, say, an internal hard drive, to the extent that the host computer can format the storage device with a file system of the user's choice (FAT-12, FAT-16, FAT-32, NTFS, etc) or does the host computer interact with these devices at a higher "layer" where it does not know, or does not see, or does not have control over the file system being used by the device?

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USB devices are attached in such a way that the OS can format and use them as any other drive. They're on a special pseudo-SCSI bus that allows them to be removable, but still accessed like hard disks.

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The matter is COMPLETELY different in Window 9x/Me from NT/2K/XP/2003.

On NT based systems, the OS detects the device (on DOS based ones the BIOS is "more trusted") and loads the drivers accordingly.

Which means, as an example, that a "normal" USB stick CANNOT be "fdisked" (i.e. using Disk management) unless it is seen by the OS as "fixed", hence the use of either the "removable bit flipping manufacturer utility" or a Filter Driver, or the "special" utilities like the HP one, petousb, makebootfat, and Swissknife, on the contrary DOS/Win9x/Me will allow to use fdisk allright.

See these for some references and links:



Once a hardware "mass storage" device is recognized, if a partition or volume is found it is assigned a drive letter, then comes into play the file system recognizer driver, that checks whether the letter corresponds to a volume formatted as a known filesystem (for which a driver is installed on the system), if it is when you access the drive by double clicking on it you will see the files within it, otherways you will be prompted for formatting the volume.

Nonetheless, it is possible to access the device as RAW data with particular programs.

If you could expand a bit on the question and on its backgrounds, I may be able to give you a more "targeted" answer. :)


Edited by jaclaz
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