how to enable AHCI on windows 7

A simple reminder to myself how to enable AHCI, on a previously installed windows 7 machine.

last few days, ive been having some issues enabling AHCI on my new motherboard.. i made the mistake of installing Windows 7 x64, while SATA mode was set as IDE, and i really wanted to use AHCI as it enables NCQ and the likes..

But its not just jumping into your BIOS and selecting AHCI mode, nono, if you do so, you will hit the same wall as i did. Windows will bluescreen as soon as you try to boot after setting AHCI, as it does not load the AHCI drivers.. BUT REJOICE!

Cheers to a mighty fine man over at Asus boards for a simple solution, and here it comes:

AHCI (Advanced Host Controller Interface) enables native command queuing and hot-plugging through SATA host controllers (Serial-ATA) for your hard drives. In many scenarios it enables more efficient multi-tasking. Vista was the first Windows OS to support AHCI out of the box, where as Windows 7 does the same. But an issue with AHCI is that if you install the OS without enabling AHCI in the BIOS, enabling it after installation will render your OS unusable. This is because Windows disable the AHCI driver since it is not needed during the installation.

There is one way to fix this, although you need to have knowledge of registry editing. The detailed steps from Microsoft are as follows:

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_MACHINESystemCurrentControlSetServicesMsahci

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.

After this you’ll have to restart your computer, go to BIOS and enable AHCI. When you log in to Windows again, you’ll notice the installation of drivers for AHCI. Another restart will be required to finish the driver installation.

Pretty simple when you think of it!