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The MSDN page: CreateFile has some help on this function, and if you scroll down (quite a long way) it will have links to CloseFile, ReadFile, WriteFile, etc.

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Mats

Just use CreateFile() with the devicename (e.g "H:" itself).

Edit: You may want to disable autorun, so that Windows doesn't open the device - you can only open a raw device if nothing else has it...