If you are planning on switching over to an SSD or just want to take advantage of hot-swap SATA drives in Windows 7 you will need to make some simple registry changes first. This will allow you to boot off the drive after you have switched it from IDE to AHCI.Do this BEFORE you switch the drive.
1. In Windows 7 go to Start –> Run and type in “regedit” without the “”.
2. In regedit navigate to HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Msahci. To do this simply expand each section in the order given.
3. Change the “Start” value to 0 (zero) by double clicking on it and typing 0 and clicking ok.
4. Now navigate to HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Pciide.
5. Change the “Start” value to 0 (zero) by double clicking on it and typing 0 and clicking ok.
6. Shut down your computer.
7. When you start it back up enter your BIOS (usually the delete or one of the F keys ie F1) and switch the drive over to AHCI.
If your computer doesn’t boot just switch it back to IDE. I’ve tested this though on a few occasions and it’s worked fine. Don’t expect a performance boost though, just some new features. It is recommended for SSD drives however and may benefit performance.