How can I enable AHCI on a SATA drive after installing Windows?

"You need to make the msahci and/or IastorV drivers be loaded early.

(Note: For Windows 10, the built-in driver is called storahci.)

According to Microsoft KB 922976, run Fix it 50470 or open regedit, navigate to one of these keys:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\msahci
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\IastorV

and set the value of the Start dword to 0.

Reboot and enable AHCI in BIOS, now it should work.

Remember to create a restore point before any changes, just in case.

The same registry changes can be done via Cmd, using reg add or sc config:

Check current parameters (and make sure the service exists):

sc qc msahci

Change the boot mode:

sc config msahci start= boot

(Note that start= is a single parameter, but boot is separate.)"