Activating AHCI mode after installing Windows on IDE mode

I recently just rebuilt my home PC and installed Winodws 7 on it. It was a nice fast, smooth install and generally went without a hitch.

That is, without a hitch until I discovered I’d installed Windows whilst the motherboard’s SATA controller was in IDE mode and not AHCI mode. Why is this important? Well without AHCI you don’t get nice things like power saving, native command queuing etc and that impacts the power consumption, speed and noise of your drives.

Of course that does rely on having a drive that supports those features, since like most newish drives mine do, I wanted to benefit.

Unfortunately just changing the setting in the BIOS causes Windows 7 and Windows Vista to both blue screen (BSOD) at boot up with the error STOP 0x0000007B INACCESSABLE_BOOT_DEVICE. That’s because Windows doesn’t have the drivers for AHCI since I installed it with IDE drivers.

How to get around this? Well it’s surprisingly simple. After reading lots of hairy articles about hacking in drivers etc I found this knowledge base article http://support.microsoft.com/kb/922976. One simple registry setting and Windows enables it’s default AHCI driver. You can then reboot, change your BIOS settings from IDE to AHCI and Windows will boot and redetect your controller and drives.

Once that’s done, I rebooted to finish the install, then I installed the Intel Matrix Raid drivers so I had the actual manufacturers drivers on rather than the generic Windows ones.

All sorted now and it saved me a reinstall. I’ve just done a copy of 20GB of data from partition to partition on the same drive, much faster and quieter with AHCI than without. I guess that’s down to NCQ being able to reorder the reads and writes into something a bit more effiicient.