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 EVGA.com, “…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.
WARNING: This tip requires editing the Windows registry. If you don’t know what you are doing or do not feel comfortable doing this, please do not attempt. Making changes to the registry can result in performance issues or even damage your Windows installation.
Here we go:
In the Windows start menu search box type regedit, then right-click the entry and click Run as Administrator.
In regedit, navigate to HKEY_LOCAL_MACHINESYSTEMCurrentControlSetservices, 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.