Switching your SATA hard drive from IDE to AHCI

AHCI (for Advanced Host Controller Interface) is a standard defined by Intel for operating SATA devices (see Wikipedia for some technical gibberish ;)). Bottom-line is, switching an SATA hard drive from IDE to AHCI will probably give you a nice speed boost, as you can see in this article (in French, sorry). It’s supported natively in Windows Vista/7 and Linux starting with kernel 2.6.19.

From what I read, there are many potential issues for switching from IDE to AHCI under Windows XP and Vista, and I can’t test those so I just won’t cover them. Basically on Windows XP you’ll need to install AHCI drivers, on Windows Vista you’ll need to apply the latest updates.

For Windows 7, the drivers are already there, but you need to activate them. That is, if you install Windows 7 on a drive already configured in AHCI, you have nothing to do, all will be handled automatically, but if your hard drive was configured in IDE when you installed Windows 7, then you’ll need to enable AHCI drivers manually. To do so:

• Launch regedit (hit start button, type “regedit” and hit enter)
• Navigate to the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\iaStorV key, and change the Start value from 3 to 0
• Do the same with key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\msahci

That’s it, your Windows 7 is now ready to run on an AHCI drive. Now you just need to make the switch from IDE to AHCI in your BIOS.

Source: Microsoft Knowledge Base – Error message when you start a Windows 7 or Windows Vista-based computer after you change the SATA mode of the boot drive: “STOP 0x0000007B INACCESSABLE_BOOT_DEVICE”