How host applications access a device depends on the driver the host assigns. For example, most OSes assign a drive letter to each mass-storage device. Windows treats all HID keyboards as a single device, though applications can use Raw Input to access a specific keyboard. For generic HIDs (not keyboards or mice), applications can open a handle to each HID interface.
If you need to keep track of which device is which even after rebooting or detach and reattach, you'll need to use serial numbers or other vendor-defined, device-specific data.
Thanks for posting your question!
Jan
