AHCI - DON'T Forget it!

Tang · 22 Mar 2010

I am planning a fresh install of W7 x64 to help clear the slate on some odd occasional issues that popped up on my system. In some of my reading, I learned a VERY LITTLE about AHCI. Setting it in the bios BEFORE installing the OS- as opposed to turning it on afterward an install can be kind of a pain in the butt. AHCI can increase performance on SSD drives and that's what brought it to my attention.
That, is the extent of what I know about Advanced Host Controller Interface.

So what do I need to know about AHCI? Why not turn it on for any computer with SATA drives before installing the OS? SSD or standard spinning drives...

JimLewandowski · 22 Mar 2010

Native Command Queuing (NCQ) is the potential "benefit" of AHCI. The hot-plug and power stuff is kind of moot.

NCQ seems more applicable to servers vs. desktops. Don't worry about it. I'd like to learn more about controller microcode to see what can be done from the OS side to speed up I/O operations (read-ahead, etc.).

gregrocker · 22 Mar 2010

The rule of thumb for Win7 installs is to first try SATA controller set to ACHI in BIOS setup, then if it won't install use IDE.

Some cannot install without ACHI, others cannot install with it - it is chipset dependent.

pebbly · 23 Mar 2010

you can always read BFK's excellent tutorial AHCI : Enable in Windows 7 / Vista :)

Tang · 24 Mar 2010

Is the explanation just that simple? The we pretty much should always look for this these days before we install an OS! It should be listed as part of the list to check off right next to making sure you have all the drivers you need for your MoBo. Man- I wasn't looking and the world changed on me again!

pparks1 · 24 Mar 2010

I think that AHCI is a tossup depending upon your hardware. For example, on my computer with a Gigabyte GA-EP45-UD3R Rev 1.1 mobo with the F9 BIOS...when you enable AHCI you are presented with an 8 second delay on each and every reboot as the system initializes the controller. In addition, with tools such as HDTune and HDTach, when AHCI is enabled my read and write speeds drop by a few MB/s.

And the "potential benefits" from NCQ don't seem to actually make hardly any difference whatsoever based on a bunch of timing tests, reboots, and benchmarks.

Therefore, I know that I lose exactly 8 seconds at each boot and I don't believe that I gain those 8 seconds back within an hour or two of using the computer from NCQ.....so for this reason I leave my computer in IDE mode and feel it provides the best performance with my configuration.

dustywoodworker · 02 Sep 2011

It has already been stated that AHCI is more or less dependent upon the platform that you are using. When I had trouble installing W7, I was repeatedly asked if my SATA Controller was set to AHCI or IDE. Apparently, my controller takes care of that itself.

I assume that I am but my BIOS does not offer those options (AHCI or IDE).

DeaconFrost · 02 Sep 2011

AHCI for an SSD drive is a given, because it allows the Windows 7 installer to recognize the SSD and configure itself for an SSD on the fly. As for spinners, I doubt it makes much difference, but I never saw a reason not to use AHCI. I only use Intel-based chipsets, so there's never any extra drivers to load during the install. Always seems straight-forward to me.