Consider the following scenario. You have two Serial Advanced Technology Attachment (SATA or RAID) hard disks attached to channels SATA 0 and SATA1 on a Windows Vista-based, a Windows Server 2008-based, a Windows Server 2008 R2-based, or a Windows 7-based computer. However, Disk 0 may not be assigned to the hard disk on SATA 0, and Disk 1 may not be assigned to the hard disk on SATA1. You expect the disk-assignment numbers to match the corresponding SATA or RAID channel numbers.

When you set up Windows Vista, Windows Server 2008, Windows Server 2008 R2, or Windows 7 on a computer that has multiple hard disks, you may experience this problem. Because you expect the disk assignment numbers to match the corresponding SATA or RAID channel numbers, you may set up Windows Vista, Windows Server 2008, Windows Server 2008 R2, or Windows 7 on the wrong drive, or you may even try to format the incorrect drive partition. Therefore, you may lose important data.

Additionally, when you install Windows 7, the installation creates a 100MB system partition alongside the Windows partition by default. The system partition is created to accommodate a Bitlocker requirement. Bitlocker requires that the boot files and Windows files are located on separate partitions. By default, the 100MB system partition is created on the disk that is detected as Disk 0. If you install Windows to a disk other than Disk 0, the 100MB system partition will still be created on Disk 0 during the installation.

You can see the assigned disk numbers by using any of the following methods:

• Run the Disk Management console. To do this, click Start
  Collapse this imageExpand this image

  
  , type diskmgmt.msc in the Start Search box, and then click diskmgmt.msc in the Programs list.
• Use the Diskpart.exe command-line utility to run the list disk command.
• During Windows Vista, Windows Server 2008, Windows Server 2008 R2, or Windows 7 setup, the assigned disk numbers are listed when you are prompted to select a drive and a partition for the installation.

Note Under certain circumstances, it may be difficult to notice that the disk numbering does not match the corresponding SATA or RAID channel numbers. For example, if both SATA or RAID hard-disk sizes are identical, it may be difficult to tell the disks apart by using these methods.

The disk-assignment numbers may not necessarily match the corresponding SATA or RAID channel numbers. There is no assurance of a consistent relationship between PnP enumeration and the order of the hard disks that are detected during setup. Devices are presented in the order in which they are enumerated. Therefore, the disk-assignment numbers may change between startups. For example, assume that you run Windows Vista, Windows Server 2008, Windows Server 2008 R2, or Windows 7 Setup on a computer that has two unformatted SATA or RAID hard disks. In this situation, Windows may present the second hard disk as Disk 0 when you are prompted for the disk on which to install Windows Vista, Windows Server 2008, Windows Server 2008 R2, or Windows 7.

When you set up Windows Vista, Windows Server 2008, Windows Server 2008 R2, or Windows 7 on a computer that has multiple SATA or RAID hard disks, verify the disk drive on which you will set up Windows Vista, Windows Server 2008, Windows Server 2008 R2, or Windows 7 by checking the disk information. For example, on the screen that lets you select the drive for the setup destination, verify the volume name and the available space.

Note You may not experience this problem when the Setup program runs on your computer. However, you may experience the problem if you configure Windows Vista, Windows Server 2008, Windows Server 2008 R2, or Windows 7 during installation or if you perform a recovery process that was provided by the computer manufacturer or this symptom can occur during normal Operating System start up as well. Therefore, hard disks may have different disk numbers across boots on a system. 

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

For more information about a related issue, click the following article number to view the article in the Microsoft Knowledge Base: For more information about PnP enumeration and hard disk drive letter assignments in Windows Server 2003 and Windows XP, click the following article number to view the article in the Microsoft Knowledge Base: