Convert SATA IDE to AHCI on Vista?

Consider the following scenario. In the BIOS setup of a Microsoft Windows 7 or Windows Vista-based computer, you change the Serial Advanced Technology Attachment (SATA) mode of the boot drive to use the Advanced Host Controller Interface (AHCI) specification. You then restart the computer. In this scenario, you receive the following error message:

STOP 0x0000007B INACCESSABLE_BOOT_DEVICE

This issue occurs if the AHCI driver (Msahci.sys) in Windows 7 and Windows Vista is disabled. This driver must be enabled before you change the SATA mode of the boot drive.

Important in This method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

322756 How to back up and restore the registry in Windows

To resolve this issue, enable the AHCI driver in the registry before you change the SATA mode of the boot drive. To do this, follow these steps:

1. Exit all Windows-based programs.
2. Click Start, type regedit in the Start Search box, and then press ENTER.
3. If you receive the User Account Control dialog box, click Continue.
4. Locate and then click the following registry subkey:
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Msahci
5. In the right pane, right-click Start in the Name column, and then click Modify.
6. In the Value data box, type 0, and then click OK.
7. On the File menu, click Exit to close Registry Editor.

During the Windows 7 or Windows Vista installation process, any unused storage drivers are disabled. This behavior speeds up the operating system's startup process. When you change the boot drive to a driver that has been disabled, you must enable the new driver before you change the hardware configuration.

For example, assume that you install Windows Vista or Windows 7 on a computer that contains a controller that uses the Pciide.sys driver. Later, you change the SATA mode to AHCI. Therefore, the drive must now load the Msahci.sys driver. However, you must enable the Msahci.sys driver before you make this change.

This issue affects only the boot drive. If the drive that you change is not the boot drive, you do not experience this issue.

AHCI provides several features for SATA devices. These include hot plug functionality and power management functionality. For more information about the AHCI specification, visit the following Intel Web site:

http://www.intel.com/technology/serialata/ahci.htm

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