Changing from IDE Emulation to AHCI

Recently, the second [Media only] hard drive in my HTPC started to fail – my Wife heard lots of good old clicking coming from it. So I checked the SMART status – which reported OK, but there was clearly something wrong with the drive. I also happened to be looking in the BIOS just to make sure everything was OK, and I noticed that all of the SATA ports were set for IDE emulation mode! While I doubt there is any real performance benefit, I like the idea of NCQ, hot-plugging, and individual drive power control. So I immediately changed to AHCI mode and rebooted, only to have the system continually reboot. I have had this happen before, and always thought that if you wanted to use the other type of controller, you had to enable it before installing Windows. Turns out that’s not true!!

**Note- this only works with Windows Vista or later OSs – XP does NOT natively support AHCI controllers**

To switch SATA controller modes to AHCI, the system must already boot – so in my case, I had to reset the BIOS to IDE mode and boot the system. Next, open the registry and navigate to the following location:

HKLM > System > CurrentControlSet > Services > msahci

Modify the ‘Start’ key to decimal zero. Then, reboot the system, enter the BIOS, and change the controller mode to AHCI. After booting the system, it will detect a new type of controller, install the appropriate drivers, and request a reboot. Done! More info is available here: KB922976

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