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Posted By Subodh on Sunday, January 10, 2010
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Installing Windows 7 on iMAC 27" Core i5/i7 is a breeze.

The new iMac with its 27” LED display and core i7 goodness, slim profile and drop dead gorgeous looks lacks just one thing. It doesn’t run Windows 7 out of the box. Snow Leopard and the lackluster  Apple supplied software notwithstanding, I was still drooling at how big a code window I could get if I fired  up Visual Studio 2010 in this baby. Here’s a step by step guide to matching the most beautiful (if not the best) hardware with the most useful OS of all times – Installing Windows 7 on iMAC 27” Core i5/i7.

A word of caution before you proceed further. This post is provided as is with no warranties. You are responsible for your own actions if you goof up. Do not attempt this unless you have everything backed up and know how to restore an OS back from the dead.

1. Fire up Bootcamp

Start Bootcamp

Less than 5 minutes after setting up the iMac, I hit the spotlight and saw Bootcamp comes pre-installed on Snow-Leopard. How nice of Apple. Fire it up and partition your hard disk!

2. Partition your HDD

Partition your iMAC HDD as needed

The iMac ships with a 1 Tb of hard disk space that gives you enough freedom to choose how much you need. Just be careful, you still need to leave enough for Snow Leopard to run (if you intend to leave it). Anyway, create a partition for Windows and hit the “Partition” button.

Insert your Windows 7 installation disk

Insert your Windows 7 Installer disk and reboot.

Since at this point I’m feeling quite empowered and happy, I chose to ignore the 32 bit requirement thrown in by BootCamp, I just opted for a 64 bit version of the Windows 7 DVD. Clicking on “Start Installation” just reboot the iMac and you can see the Windows 7 installer firing up without delay.



Now, I would have expected BootCamp to mess up the partitioning a little but not so much as not even labeling the Windows partition as Windows. In any case, since I knew the approximate size of partition I created was the largest, I could identify which partition it exactly was that I need to install Windows upon. Pay attention here lest you might lose your Snow-Leopard install itself

Be a little cautios and find exactly which is the partition you need Windows installed upon

Once you are done clicking through, let Windows do what is one of the best OS install procedures. No Mac, no Linux, no other installation comes even close to the finesse with which Windows 7 installs!

Windows 7 installation

Of course, the joy will be short lived, what with Apple’s choice to use ATI display adapter instead of NVIDIA. Once Windows shows the prompt to “Preparing Windows for first time”  the Screen goes blank. Apparently Windows thinks the DisplayPort is the Primary display (not the built in display) and the screen will just go blank. No need to panic, just power off by holding the power button and hit Option (Alt) key while the iMac boots up. You would be presented with the Boot Options screen. Select the Windows Installation DVD you were installing from.

Select the Windows 7 installation DVD


Leave everything to default and hit Next

Leave the selections as is. Hit Next.


On the next screen Click “Repair your computer”

Choose Repair your computer


After what seems like eternity, Windows will find the partition you were installing upon and present you with the option (you really have to just click next!) to choose the partition you need to repair.

Choose Repair your Windows 7 partition

On the next screen choose “Command Prompt”

Choose Repair in the command prompt mode.


As I said before, it doesn’t take much for Windows to recover from a disaster. In this case, there was no disaster (Windows was just showing the primary display on another port) so we have to create one. Change the directory to C:\ and change directory to C:\Windows\System32\drivers

Delete all ATI driver files by using del ati*.sys

Delete all ATI drivers from the Windows driver directory


Once you’re done, you can exit and reboot gracefully or if you’re a jerk like me, just hit the power button and let windows start again. Just make sure you’re connected to the network (and I always have a DHCP server running).

Windows is preparing .. for a 2nd time.

Voila! Just like magic, Windows 7 will not just recover from whatever you did just now, it would also download and install the latest ATI driver from Windows Update as soon as you’re done entering the basic information



Windows 7 downloads the ATI driver as soon as you're connected.

Completing the Windows 7 Installation

You would be surprised to find out that Windows 7 actually installs drivers that are of a higher version than that provided by the iMac installation DVD. The Apple recommended procedure is to insert the Mac OS DVD again after Windows installation is complete to install the drivers for Mac hardware but when I tried doing that, I realized I would be downgrading the drivers. So, for me, there was no need to install anything from the iMac DVD. Everything I needed was installed automatically by Windows Update except of course; BootCamp itself.


You do need BootCamp, primarily to lower the screen brightness. The only thing that does not work is the auto brightness sensor and even after you install from the BootCamp drivers, it still would not work. My solution so far has been to manually reduce the brightness using BootCamp control panel(or system tray) icon. Everything else, including the Bluetooth and the iSight camera work perfectly fine on the x64 version of Windows 7. BootCamp is also needed if you need to switch back to Mac OS often (without requiring you to hold on to the Option key while booting). Just click on the BootCamp icon and choose Reboot in Mac OS.

So, there you go! Happy Windows on iMac. Let me know if this worked/ did not work for you in the comments.

Windows 7 running on iMac 27". I'm loving it!


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 Comments & Discussions

  • Gravatar
    Ph0eniX Wednesday, January 13, 2010 at 3:43 PM

    Thank you very much for this elegant workaround; you just spared me hours of wandering !

  • Gravatar
    guru tugginmapuda Sunday, March 14, 2010 at 6:09 AM
    thanks 4 the qu1ck t1p!
    just installing windows 7 and got the blank screen, thanks for the tip to get around it.

    nice <@happy

  • Gravatar
    Sgt_Pepper Wednesday, July 14, 2010 at 1:00 PM

    Thanks a lot!!!

  • Gravatar
    Amaj Friday, July 16, 2010 at 5:40 PM

    you're a lifesaver, my parents didn't want to spend the 125 dollars to have someone else install windows 7 and they thought i broke the computer and it looked like i would have to pay the 2000 bucks to replace the computer

    • Gravatar
      Subodh Friday, July 16, 2010 at 6:30 PM

      I'm glad it worked out for you!

  • Gravatar
    adolfo Wednesday, August 04, 2010 at 6:44 AM

    how i deleted that files if Im using a Nvida card, I have and imac 21.5 Late 2009

    • Gravatar
      Subodh Monday, August 30, 2010 at 7:20 PM

      This article is not for you happy Don;t delete anything.

  • Gravatar
    duppy Tuesday, August 24, 2010 at 5:06 PM

    Hi, thought you might be able to help - I have a new iMac i7 and have tried installing Window 7, all went well except when I checked the Windows information I installed the 32bit version so can only access 3gb of my 8gb RAM. Tried doing a clean install with Bootcamp but in the installation I can't see an option to install 64 bit version of Windows? Text says Windows 7, Architecture x86. IN your post you said you chose between versions?

    I just opted for a 64 bit version of the Windows 7 DVD.

    Where was this option in the Windows install?

    Thanks heaps,

    • Gravatar
      Subodh Tuesday, August 24, 2010 at 5:27 PM

      Couple of things I can think of:
      1) Are you sure you're trying to install x64 version of Windows 7?
      2) My version of the Windows 7 had multiple versions, your DVD installer may be different.
      3) If you use the serial key /license key, I've seen certain version auto-select the kind of installation you've purchased license for. Its best to wait 30 days and only activate when you're sure your installation is good.
      4) Doesn't sound like this is an upgrade. If it is, you cannot upgrade from x86 to x64


      • Gravatar
        duppy Tuesday, August 24, 2010 at 5:49 PM

        Hi Thanks a lot for your fast reply.

        1 - Yes I know the DVD has Windows 7 64 bit on it, and my computer running Windows 7 32bit is 64bit capable after running the Performance test option in the control panel.
        2 - Yeah mine had different versions too - but when it came up all were listed as x86 Architecture. Im assuming that 64 bit would be x64 - is this right?
        3 - Thanks will give this a try.
        4 - Yes correct this isn't an upgrade, a clean install.


  • Gravatar
    Andy-S Monday, August 30, 2010 at 12:15 AM

    Why didnt i think of that !!!!!!!!! You're a genius..Thanks.

  • Gravatar
    Sam Thursday, December 02, 2010 at 3:03 PM

    Tried everything you said but cant find the ati*.sys anywhere

  • Gravatar
    avl412 Saturday, December 04, 2010 at 1:22 AM

    i tried installing win7 but in the end it says i have to restart the installation. help plz i did everything u listed

  • Gravatar
    resume writers Sunday, December 05, 2010 at 7:10 AM

    Well, it's clear that Mac will never be supplied with pre-installed Windows but at least there are no problems installing it if you prefer Win7 to MacOS

  • Gravatar
    Lee Wednesday, February 02, 2011 at 8:22 PM

    thanks so much. you save me and my computer!! happy

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