What happens if after turning on AHCI in a Lenovo systems Bios you get a Blue Screen of Death when Booting into Windows? The only way to boot back into Windows is to turn off AHCI putting the setting back to Compatibility mode. Is there a fix for this without having to reload Windows with the AHCI setting turned on?
Note: This is only a fix for Windows Vista and Windows 7. XP users will still need to toggle to compatibilty mode in BIOS.
As a bit of background on this subject:
In the system BIOS, AHCI enables NCQ (Native Command Queueing) and hot-swapping of current-generation SATA hard drives. Enabling AHCI with SATA drives that support NCQ will provide higher performance in some cases by allowing the drive to optimize the order of read and write requests based on the position of the platter, reducing head movement and enabling the drive to serve requests in fewer rotations over time.
However, AHCI should be enabled in the BIOS prior to OS installation. Turning it on after you’ve installed the OS will usually cause the BSOD symptom often described or hang the PC upon boot. This happens because Windows disables the AHCI drivers not needed during installation, so if you turn on the feature, the driver won’t be there at boot up and the system will crash.
Fortunately for Win7 and Vista there is a fix:
1. Back up your Registry before applying this fix.
2. Exit all Windows-based programs, click Start>Applications> Run, and type regedit and then press ENTER.
3. If you receive the User Account Control dialog box, click Continue.
4. Navigate to the following Registry subkey: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Msahci
5. In the right pane, right-click Start in the Name column, then click Modify.
6. In the Value data box, type 0, and then click OK and exit the Registry Editor.
7. Restart your PC and enter the BIOS menu at POST. Enable AHCI in your BIOS.
8. At boot-up, Windows will install the AHCI drivers and ask you to reboot your machine one more time.
You have completed the fix without having to reload the Operating System!