How to enable AHCI in Windows 7 after installation as ATA

OS Windows 7

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.