Tutorial : How to switch from IRRT to AHCI mode - E6400/E6500 (Vista)

If you're still using the Dell factory Vista image that came installed on your notebook, you can simply change the bios setting from IRRT(default) to AHCI and reboot. The Dell image already contains the AHCI drivers and enum info, so nothing to see here move along

Issue

If you reinstalled Vista at some point while the system bios was in IRRT mode (default as shipped from Dell) and later tried to change to AHCI you'll find that the system blue screens booting into Vista.

Microsoft kb922976 says you need to enable the native MS AHCI driver in the registry for this to work, but you'll quickly find out that it's not so simple and the system still blue screens going into Vista.

Why switch from IRRT to AHCI ?
IRRT mode introduces some issues and added latency to the system. I suspect this is caused by the Intel raid monitor drivers constantly polling the ports for raid drives, which I also beleive reduces battery life. Intel tried to fix that with the 8.7 drivers, but that seems to cause other issues including more latency spikes and poor audio.

I've also found that AHCI improves boot speed and overall responsiveness of the system is considerably improved. No scientific basis, just personal observation.

Cause
I had some time over my morning coffee to figure out why the MS kb fix doesn't work and how to fix it.

The problem stems from the fact that Vista can't properly identify the GM45 AHCI SATA ports because this chipset is only a few month old and Vista doesn't know what to do with it on detection.

Solution
The solution is to help Vista identify the chipset, then let it load the default MS AHCI drivers so it can boot into Vista and then you can install the Intel AHCI drivers.

How to

Disclaimer: This involves making some minor changes to the system registry so the usual be careful disclaimers apply. Backup your system first and if you don't know what you're doing get a friend who does to help you. Proceed at your own risk.

Ok, now with that out the way, let's get started:

With the system still running in IRRT mode;

1. Safety first: Create a system restore point that you can revert to in case.

2. Download Dell's - Intel 8.2.2.1001 SATA driver application to your desktop. Don't run it yet, you'll need it later.

3. Click on start and type regedit in the search box. Select the registry editor program on the menu.

4. Follow the steps in MS kb922976
-In the registry navigate to;
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Msahci

-In the right pane, right-click Start in the Name column, and then click Modify.

-In the Value data box, type 0, and then click OK.

-On the File menu, click Exit to close Registry Edito

5. Now we need to add Intel's GM45's AHCI enum info to the registry so Vista can identify it on startup (so it doesn't bluescreen)

We do this by adding the following key

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\CriticalDeviceDatabase\PCI#VEN_8086&DEV_2929&CC_0106]
"ClassGUID"="{4d36e96a-e325-11ce-bfc1-08002be10318}"
"Service"="iaStor"
"Security"=hex:01,00,04,90,00,00,00,00,00,00,00,00,00,00,00,00,14,00,00,00,02,\
00,4c,00,03,00,00,00,00,00,14,00,ff,01,1f,00,01,01,00,00,00,00,00,05,12,00,\
00,00,00,00,18,00,ff,01,1f,00,01,02,00,00,00,00,00,05,20,00,00,00,20,02,00,\
00,00,00,18,00,9f,01,12,00,01,02,00,00,00,00,00,05,20,00,00,00,21,02,00,00

But that's a lot of numbers to enter manually, so I've created a reg entry and attached it to this post to make it much easier. Just unzip it to your desktop (you can right click and select edit if your paranoid and want to see the contents). Otherwise just right click on the file and select Merge to add the keys into the registry.

Or you can cut and past the above and create your own registry key.

6. Now that the system knows to start the msahci driver on startup and with the reg entry in #4, it can properly identify and enum the GM45 AHCI chipset. In case you're wondering PCI#VEN_8086 is Intel.

-Shutdown the system.
-Boot into the bios by pressing F12.
-Change the SATA mode from IRRT to AHCI in the bios, APPLY and exit.

System will boot, but might take a short while longer while it dectects the new chipset for the first time and then boots to the Vista desktop.

7. At this point, you'll see an icon in the system tray showing new device detected installing drivers. This is installing the MSACHI drivers. After it's done DO NOT RESTART yet, even if it asks you to.

Find the Intel SATA driver application you downloaded in step 2 and run it.
It'll detect the system in AHCI mode and install and setup the appropriate drivers. Once done go into device manager and you'll see the Intel (R)ICH9M-E/M SATA AHCI Controller now listed and running correctly.

8. Restart your system

If anything went wrong along the way, you should just be able to change the bios setting back to IRRT and run system restore which created in Step 1.

After these steps, you'll be able to switch back and forth between IRRT and AHCI as you please, both can now be correctly identified by the system.

Hope you'll find this info useful

 

@MiB - I'm assuming that your instructions are appropriate for the M4400 as well (since the machines are mostly the same). Thank you for the howto - very informative, and just what I was looking for.

 

Worked for me!

THANK YOU SO MUCH! I was looking for this since I bought my e6400 in October.

Is there a way to switch to ATA without reinstalling?

 

Excellent Tutorial.

Greg

 

Yes it should work just fine for the M series as well.
I say should because I haven't tested it myself but I'm quite certain it's the same Intel GM45 chipset as the E series Latitude.

In fact it should also work for any notebook using the GM45 chipset like the Lenovos, but shhhhhh

 

Ehm...is this all necessary!?!

When i switched from IRRT to AHCI i just did so in the BIOS and done.

 

I'm guessing that your OS is Dell installed. I have an aftermarket hard drive with a clean Vista install. When I changed to AHCI in the BIOS, I immediately got a BSOD because Vista did not recognize the controller. In my case this howto is an absolute must.

 

You're very welcome, glad it helped.

Haven't looked into what's needed to go to basic ATA, but I don't think you'd want to downgrade to ATA mode anyways as you'd lose SMART, hot plug eSATA and enhanced power savings features that you'd get with AHCI.

 

Yes, unfortunately Vista predates the GM45 chipset so it can't properly identify it if you switch from IRRT to AHCI on a reinstalled OS.

The Dell factory image has this enum info slipstreamed in so you wouldn't need to make any modifications other than change the bios setting.

I think it was clear in the tutorial why and when this applies, but maybe not

 

ATA is good for SSDs. They perform a lot better than in AHCI Mode.