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Windows allows you to assign a certain letter to an external disk drive (using diskmgmt.msc). Whenever the device is plugged in again, it assigns this same letter again.

How does Windows identify this device as being the same? What kind of (unique?) identifier does it use?

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migrated from Aug 18 '10 at 13:41

This question came from our site for system and network administrators.

It will use a Universally unique identifier (UUID). You can find out more about UUIDs here. The UUID of the device will be associated with the drive letter.

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Yeah, i know about UUIDs. But where exactly is this UUID? Is it part of any file system, part of NTFS, part of whatever? – Christian Aug 18 '10 at 8:12
AFAIK it's in the footer on the drive. – Shinrai Aug 18 '10 at 14:32

The file system includes a (statistically) unique id. I assume Windows remembers those.

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Windows stores a GUID/UUID in a disks's MBR (reference). This is stored and referenced in the BCD which the Windows Boot Manager uses, and I guess the rest of Windows uses that too. Disks formatted to the GPT standard have a spot to hold a disk GUID or UUID (reference) which I would surmise is used in the same way by Windows.

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