Activate AHCI in Windows

Check the SATA mode in BIOS. AHCI mode was disabled and the machine was running on RAID. Windows 7 performs much better with the AHCI mode enabled. But that did not work as the AHCI drivers were not loaded at time of installation. The system would not recognize the HDD and I would get the Error: 'STOP 0x0000007B INACCESSABLE_BOOT_DEVICE'. The cause is Windows 7 will only install the AHCI drivers at installation if the mode is enabled at the time of installation. So boot in RAID mode and manually enabled the AHCI driver in the Windows Registry. This process is as follows:
Enable the AHCI driver in the registry before you change the SATA mode of the boot drive.
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 one of the following registry subkeys:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Msahci
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\IastorV
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.
The MIcrosoft KB link for this is here: http://support.microsoft.com/kb/922976
Restart and go into BIOS. Change the mode to AHCI and this time the boot was successful.
Source: https://community.spiceworks.com

Error message occurs after you change the SATA mode of the boot drive

Applies to: Windows Vista BusinessWindows Vista EnterpriseWindows Vista Home Basic More

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Symptoms

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After you use the BIOS setup of a Windows 7-based computer or a Windows Vista-based computer to change the Serial Advanced Technology Attachment (SATA) mode of the boot drive to use either the Advanced Host Controller Interface (AHCI) specification or redundant array of independent disks (RAID) features, you receive the following error message when the computer is restarted:

STOP 0x0000007B INACCESSABLE_BOOT_DEVICE

Cause

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This issue occurs if the disk driver in Windows 7 or Windows Vista is disabled. This driver must be enabled before you change the SATA/RAID mode of the boot drive.

 Important This section, 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 one of the following registry subkeys:
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Msahci
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\IastorV
5. In the pane on the right side, 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.

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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 is 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, go to the following Intel website:

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

Microsoft provides third-party contact information to help you find technical support. This contact information may change without notice. Microsoft does not guarantee the accuracy of this third-party contact information.The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, regarding the performance or reliability of these products.
Source: support.microsoft.com