To enable AHCI (Advanced Host Controller Interface) after Windows 7 is installed with ATA mode, do the following:
- Start Windows 7
- Run Registry Editor
- Go to: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Msahci
- Change the “Start” value from 3 to 0
- Reboot and go to the BIOS immediately
- Set BIOS to AHCI
- The next time Windows 7 loads, it will auto-detect the AHCI setting and install the drivers/devices it needs for proper AHCI operation.
Note: eSATA drives require SATA Operation in the BIOS be set to AHCI for proper eSATA operation.