I’ve been upgrading quite a few machines from Windows XP to Windows 7 lately, and for some reason, almost every time, I forget to change the SATA Operation setting in the BIOS from ATA to AHCI after wiping the drive and before installing Windows 7.
AHCI (Advanced Host Controller Interface) is a new interface specification that allows the SATA controller driver to support advanced features that can give better performance out of SATA hard drives, especially in Windows Vista/7.
After two or three times of restarting the Windows 7 installation process after changing the SATA Operation to AHCI in the BIOS, I thought their must be a way to make this change without having to reinstall Windows. After a little digging, I found out their is a simple registry change that can be made that will allow for the SATA Operation change. Here’s what you can do:

Start “regedit.exe”
Browse to HKLM\System\CurrentControlSet\Services\msahci\
Change the DWord value named “Start” from “3” (ATA) to “0” (AHCI)
Shutdown the computer
Power the computer back on, making sure to enter the BIOS and change the SATA Operation to AHCI
Save the change

Justin

Warning: Changes made to the Windows registry happen immediately, and no backup is automatically made. Do not edit the Windows registry unless you are confident about doing so. Creating a backup before editing the registry is highly recommended.