You have to enable the driver in the registry
If you like tinkering with computers a lot, you might just end up causing your computer not to load! I recently was playing around in the BIOS on my Windows 7 test box and ended up getting the following error message after restarting my computer:
STOP 0x0000007B INACCESSABLE_BOOT_DEVICE
Luckily, I knew it was something that I had changed in the BIOS that ended up causing this problem. If you have SATA drives on your computer, you probably want to use Advanced Host Controller Interface (AHCI) on your SATA host controller.
In the BIOS, you can usually choose which mode you want the SATA controllers to use, i.e. PATA (Parellel ATA), standard AHCI, or some type of vendor-specific RAID.
If you go into the BIOS and see that you are not using AHCI for your SATA drives and decide to switch to it for maximum performance and data transfer, you will probably end up getting this error after you try to restart.
Basically, before you can switch to AHCI in the BIOS, you need to enable the AHCI driver (msahci.sys) in Windows 7 or Windows Vista.
Ok, so the first thing to do in order to use AHCI is to go back into the BIOS and set the mode back to the original setting you were using so that you can load Windows back up.
Once you get back into Windows, click on Start and then type in regedit into the search box and press Enter.
Now navigate to the following registry key in Windows 7:
Now right-click on the Start key in the right-hand pane and click Modify. Change the value to 0 and click OK.
Now exit the registry restart your computer. Go back into the BIOS and re-enable AHCI mode for your SATA controller and you should be good to go!
The reason this happens is because by default when Windows 7 or Windows Vista is installed, any unused storage drivers are disabled in order to improve performance. In order to use them, you first have to enable the driver in the registry.
AHCI is better because it provides benefits like hot plug functionality, power management, and faster access to data. Enjoy!