Late 2009 27" iMac support for Win8

I had Windows 8.1 running on my iMac 27" Late 2009, sound included so i can assure you the OS works on this computer. This copy of Windows 8.1 was installed (updated) from a Windows 8 installation that i had on the iMac before.

(I first installed Windows 8, Installed latest Bootcamp 5.0.5033 and then updated to Windows 8.1)

At first, Bootcamp 5.0.5033 is not "compatible" with this model of iMac but i managed to install it anyway following this guide: http://www.iphoting.com/blog/archives/830-Boot-Camp-on-Older-Intel-based-Macs.ht ml (Note that in Bootcamp 5.0.5033 there is no "Bootcamp64.msi" file but a "Bootcamp.si" one)

However, these days i have removed Windows 8.1 from my hard drive (need to reformat the partitions because i got a new SSD) and when tried to install it again from scratch (after so much researching on EFI and ways to install it properly as SSD + HDD combinations cause problems with Windows on Mac...) i did it with a Windows 8.1 installation USB (Not an update from Windows 8 as previously described) and the first thing i noticed is that you MUST disable automatic driver download when configuring Windows for the first time, if you don't do this you will get a black screen shortly after login on Windows for the first time (It looks like Windows downloads a wrong graphic driver). I tried to install BootCamp 5.0.5033 again following the same maethod, it installed but when i restarted the system, Windows 8.1 refused to boot showing the following error:

This is related to a bad driver or hardware incompatibility so i think that the temporary workaround to get Windows 8.1 on this iMac working properly is to install Windows 8 first, then Bootcamp 5.0.5033 as mentioned above and then update to Windows 8.1 from the Windows Store. Is this or trying to install the individual drivers manually and know which are the working ones and which could cause such error.

I'll be trying both methods in the next couple of days so i'll update this thread when i got news.

There's a BootCamp specific ASC here which might be the best place to ask your question. There have been questions there about 8.1 compatibility but since I have no interest in moving beyond Win7 at this time I've not paid any attention. So check out the BootCamp threads and hopefully you'll get your answer there.

I have an identical situation to you. Ran Windows 8 perfectly since release on my Late 2009 27" iMac. Upgraded to 8.1 without a problem. Install an SSD, re-install Windows8 / 8.1 and now nothing works and suddenly my graphics card is unsupported.

That is what makes this situation so confounding, our systems ran fine until we reformated. Are they pushing out a bad driver now? What happened? What are we doing differently?

Have you had any luck with your efforts? I have had no luck yet. https://discussions.apple.com/thread/5954824?answerId=25043871022#25043871022

See here, as you highlighted, Apple only supports W7 for the late 2009 iMac ... W8 starts from the mid 2010 models and newer

http://support.apple.com/kb/ht5634

The problem is both of our iMac's ran fine for nearly two years and then when we had to re-install because of minor, nearly transparent to the OS hardware changes suddenly it didn't work anymore. Something about that seems strange to me.

Yes, i managed to install Windows 8.1 directly (No need to install Windows 8 previously) just using an thumbdrive with an EFI boot. No errors this time. I had to disable "aitomatic driver download" to prevent Windows to download the ATI drivers that causes the black screen. I also installed the latest Bootcamp with the trick mentioned above. All works great except for the video driver, i wansn't able to install an ATI 4850 drivers that works, all i have tried resulted in the same black screen..

So, Windows 8.1 installed, all working with the exception of the video card = No Windows games on this Late 2009 iMac as Windows uses a generic driver with almost no 3D acceleration...

Yeah I get the same black screen with any driver I try as well unfortunately.

Just a note to anyone attempting this:

You can enable Windows Remote Desktop when you first boot up and you'll still be able to get in and use the system even with a blank screen. If you disable automatic driver installation, uninstall the drivers for the Radeon in device manager, reboot and uninstall them again for your Radeon and reboot once more your screen will turn on. I think the key here is getting Windows 8.1 to use the WDDM 1.1 driver with the radeon, which is the only official driver AMD/ATI has released for 8.1.

So, if you use the WDDM 1.1 driver you can get 3D acceleration?

I'm not sure, but it's the only official driver for Windows 8.1.