Updating to AHCI in Windows Vista

My laptop is running Windows Vista and has a Serial ATA drive.  When Vista was installed the BIOS was set to ATA mode and not AHCI mode. 

If you simply try to change the BIOS setting to AHCI, Vista will no longer boot and you will get a blue screen “STOP 0x0000007B INACCESSABLE_BOOT_DEVICE”.

The reason is that Vista does not automatically load the ACHI driver unless it was turned on in the BIOS when Vista was first installed.  This issue can be resolved using the following steps:

  • Set the BIOS to ATA
  • When Vista boots, open regedit
  • Locate the key:  HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Msahci
  • Change the Value data box from 4 (disabled) to 0 (enabled)
  • Reboot and set the BIOS to AHCI

Windows should now start normally.

These procedures are also outlined in Microsoft KB 922976

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About jasontarby

Enterprise Architect / Network Engineer at SRA International, Inc.
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