How to Enable AHCI Support in Windows

From this site we read:
Windows 7 and Windows Vista does not install AHCI device driver if it does not detect presence of AHCI support on the system during installation. As the result, if you enable the AHCI in BIOS after Windows is installed, the system may crash and become unbootable.
If you have just notice that your motherboard does indeed support AHCI after you have installed Windows 7 or Windows Vista, but have previously been disabled, here is the trick that enable AHCI support in Windows OS. The step has to be done before AHCI is turned on in BIOS to avoid any system crash.
Type RegEdit into Start Search and hit Enter to start Registry Editor.
If the UAC dialog box prompts and asks "Do you want to allow the following program to make changes to this computer?", click Yes button.
In Registry Editor, navigate to the following registry key:
    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\msahci
In the right pane, right click on Start and select Modify.
Set the value data for "Start" to 0, and click OK.
Default value (when AHCI is disabled): 3 for Windows 7 and 4 for Windows Vista.
Close Registry Editor.
Restart the computer.
Go to BIOS configuration and enable the AHCI support. Save the settings and reboot computer again.
After system boots up, Windows will automatically install device drivers for AHCI. After installation completed, Windows will restart for one more time.
The hard disk drives are now supporting AHCI standard.

How to Check if AHCI is Enabled on Windows
If you are unsure if AHCI has been enabled or not in Windows operating system, here is a simple way to verify and determine if the AHCI is already enabled on the system.
Type Device Manager in Start Search and hit Enter.
If the UAC dialog box prompts and asks "Do you want to allow the following program to make changes to this computer?", click Yes button.
Expand IDE ATA/ATAPI controllers section.
If AHCI driver is installed in Windows, there will be entry that reads something similar to Standard AHCI 1.0 Serial ATA Controller or Intel(R) 5 Series 6 Port SATA AHCI Controller.
If you can’t find anything that specifies AHCI Controller, chance is your system don’t have AHCI support in Windows yet (if your system does support AHCI). Follow steps above to enable AHCI in Windows before turning AHCI on in BIOS level.