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How does Windows number its disks? By numbering, I mean the physical disks, which Disk Management calls Disk 0, Disk 1, Disk 2, etc.

My C and D partition used to be on Disk 0 and my E partition was on Disk 1. Now, however, my C and D paritions are Disk 1 and E is on Disk 0.

I have a backup product which backs up based on the disk numbering, so when this changes, it messes up which disk should be backed up.

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4 Answers 4

up vote 1 down vote accepted

I am pretty sure it numbers them based on their position on the ide / sata controllers. The drives should remain the same all the time unless you are switching around which ports they are plugged into.

I guess if you aren't doing that and still experiencing the problem you might look in the BIOS to see if you can fix where/what the drives are (instead of AUTO detect).

from this site

" if you have SATA and eSATA connectors with only a SATA disk connected, it will be disk 0, but if you then connect an eSATA disk, it will become disk 0, even if you are still booting to the SATA disk. A disk connected to the IDE master will always be disk 0, and the rest will re-rank."

There is no software control over this, it is all based on what the operating system reads from the BIOS.

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The disk order is defined by the IDE or SATA bus (IDE 0 or IDE 1 and SATA 0 or SATA 1) and whether the disk is a primary or secondary drive. –  Ward Jun 14 '09 at 9:59

Did you change anything physically with your hardware when this happened?

ie. did you perhaps swap ribbon cables between your drives?

If not, then it could be a flaky drive/controller

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The disks don't normally rearrange themselves unless they're being plugged into different ports (either internal or external). If you wish for them to remain the same however you can do the following:

Start->Run
compmgmt.msc
Click "Disk Management"
Right click the disk and go to "Change Drive Letters and Paths".

The driver letter you set in there shouldn't ever change.

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It depends on the version of Windows. Since Vista, the partition the OS is installed on is always (AFAIK) C:, even if it is on Disk 1 rather than Disk 0.

Under NT/2000/XP/2003 you could easily install Windows on drive D: or E: and the order of the letters was determined by the physical order of the drives.

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