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A Windows Vista hint…

Clearly this one doesn't belong on Mac OS X Hints, but I wanted to have it documented somewhere. There's usually a Windows box of some sort in my home, for testing and game playing. The testing role for my physical Windows box has pretty much been replaced by VMware Fusion, so it's really now a game playing machine.

As such, I upgraded it recently (well, rebuilt it from scratch is a better summary) with a new CPU and video card. I also wanted to put Vista on it, for one reason only: to run Crysis under DirectX 10, which only works in Vista. My Vista DVD is an upgrade installation, which must be installed from within Windows XP. Windows XP, when it came out, didn't support SATA drives, so for a fresh install of XP (it was a new install on my newly-built machine), you must set the SATA mode in the machine's BIOS to IDE. I did that, installed XP, and upgraded to Vista.

Vista includes AHCI support, so my SATA drives can be used in native SATA mode. However, if you just switch your BIOS to ACHI mode, and you were using XP in IDE mode, then your box will fail to boot -- that's because the AHCI drivers are not installed by default in Vista if you start with XP in IDE mode. So how do you switch Vista from IDE to ACHI mode?

The answer is in this Microsoft support document. You need to run the good old registry editor, regedit, and make one simple change. In regedit, navigate to HKEY_LOCAL_MACHINE » System » CurrentControlSet » Services » Msahci. Right-click on Start in the right-hand pane, and choose Modify from the pop-up menu. Change the Value box to 0, click OK, and exit regedit.

Shut down your machine, power it back up and launch BIOS setup, switch SATA mode to AHCI, and then save and boot into Windows. Problem solved. (Apparently I could have run a number of updates for XP to get AHCI support there, then upgraded to Vista. My method, though, was much faster--no need to run a slew of XP updates after install. Instead, I just launched the Vista installer as soon as XP booted for the first time.)


  1. There's a much easier solution that's been well documented:

    Install your "upgrade" DVD without using the key, which will put you in the 30-day trial mode. Then reinstall over that with the key. You never actually need to install XP.

  2. As soon as I try to run the installer when booted directly from it, I get the message "you must run this installer from within XP." I see no way to proceed past that point -- I see that message long before being asked for the key...


  3. There's a better way to do that, called "slipstreaming" and a very slick tool called nLite ( that makes the process pretty painless (well, with the caveat that it _is_ Windows). That way, should you need to install Vista, you will have an XP CD that already supports AHCI mode. Hell, you could even throw _all_ the drivers you need in there, but since you'd be upgrading to Vista anyway, not a huge deal :).

    For instance, say you had a Windows XP disk but it wasn't SP2, you could download the installer and slipstream SP2 and the AHCI drivers for your motherboard.

    There's also a vLite (linked on that same page) that is for doing the same with Vista.

    (Did this stuff for a living until a week and a half ago, now onto servers... MS servers... ah well)

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