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Sunday, July 17, 2011

How to enable AHCI in windows 7

What is AHCI?
For those unfamiliar with the term AHCI, it stands for:
Advanced Host Controller Interface
The explanation can be confusing and bit difficult depending on whom
you ask, so the simplest explanation I found was from EVGA. According to, “…it is a newer technology to provide advanced features to the
Serial ATA standard. It allows for access of the native functions of the SATA
interface such as Native Command Queuing (which allows greater
performance by optimizing how controller requests data from the hard drive)
and hot swappable of SATA devices so that you may remove SATA drives
from your PC without first having to shut down your computer.”

What is the difference?

SATA has two modes: IDE and AHCI. IDE is an older mode used with past
devices and provides the most compatibility for the older hardware.
Do I have it?
It will depend on your hardware. You’ll need to contact your manufacturer
or hardware documentation. Or do what I did and just boot into your
BIOS and check.

How do I use it?
To use AHCI, Windows requires specific drivers, which are installed during
Windows installation. The only problem with AHCI is it needs to be enabled
in the BIOS prior to your Windows 7 installation; doing so after you have
installed the OS will cause Windows not to boot. However, there is a way to
enable it after windows has been installed.
In the Windows start menu search box type regedit -> then right-click the
entry -> click Run as Administrator -> In regedit, navigate to
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services, in the left pane
click msahci, in the right-hand pane right-click Start then click Modify…
In the window that opens, change the value to 0 (zero) and click OK -> Close
the registry editor -> A restart is needed and upon boot go into the BIOS and
enable AHCI (this step will vary depending on your BIOS); when Windows
boots it will finish installing the AHCI drivers -> Another restart will be
necessary to finish the driver installation
Some user experiences, that I’ve read, with changing over to AHCI claim
higher Windows Experience Index (WEI) scores. I haven’t seen a jump in mine.
I did clock the before and after startup time for Windows and noticed a 5
second longer boot time with AHCI enabled. This might be because of AHCI
or it could just be a fluke. I’ll let you decide.

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