This question is a year old but I am going to answer it incase someone else runs into this same issue.
I just bought a mid 2011 27" refurb iMac from IBM and they scrubbed the HD completely. This eliminated pretty much every option there was for installing an OS on the Mac.
The problem is that when these models shipped they had either Lion (10.7) or at the earliest Snow Leopard 10.6.6. They are not backwards compatible with the Snow Leopard retail DVDs Apple offers, which is OS X 10.6.3. These iMacs originally shipped with installion DVDs but Apple would not send them to me.
Here's what I had to do:
Download/or otherwise obtain an OS X 10.6.7.iso file from wherever you might find something like that. It will be an disk image for a DVD not intended for this model of iMac, and it will not work.
I bought the retail DVDs (10.6.3) from Apple, and they did not work. I got a RAM Error message (three tones) at boot.
If you have both you can splice the installer package files from the retail DVDs (which work with any Mac) with the installer package files from the 10.6.7 disk image and create a "universal" OS X 10.6.7 installer disk image. This is not fancy it's a simple matter of copy and paste. Detailed instructions for this process can be found here.
After I had the modified .iso file I converted it into a .dmg using this terminal code. Again, very simple. Nothing to be afraid of.
From there I used "Carbon Copy Cloner" and Cloned the .dmg file I created through this process unto a thumb drive (needs to be at least 8gb). Worked like a charm. Just pup it in a usb port and turn on the iMac.
You can also (possibly) use Disk Utility which is a built in utility and "restore" the image to your thumb drive, but I wasn't having any luck with my Disk Utility boot disks and so I decided to try another utility. My feeling is that it likely would have worked this way if i had used DU.
Make sure your thumb is formatted for GUID. Just a word of caution. I intend to upgrade to Yosemite. The install of Snow Leopard works, but I don't fully trust it and my Airport card is non functional. Certain things went wrong in the installation process obviously, but it's good enough to boot, and then upgrade, or maybe try to install a fresh unaltered version of Snow Leopard if that's your desire.
I hope this helps someone out. I've tried dozens of different ways to just get this iMac to boot an OS and this is finally the one that worked. Apple Support was zero help. Good luck!
- I've since updated Snow Leopard to 10.6.8 and airport is now working. Everything is very smooth and functional. No problems.
An installed OS X can be specific to older models. People that administer Macs professionally call this situation "forked" and no one likes to be "forked" by surprise.
Boot the new Mac to the setup assistant (or if you have made an account there already consider making a new test user account and backing up everything on the new mac that you need to save). Then you can run the Migration Assistant and put the old Mac in Target Disk mode (TDM) instead of booting the old OS from the new Mac.
TDM works over USB-C, FireWire or Thunderbolt ports, you can connect them so that one of them appears as an external hard disk on the other. This is called “target disk mode.”
- Connect the two computers with one of the above cable types.
Start up the computer to be used as a disk in target disk mode:
If the computer is off, start it up while holding down the T key.
If the computer is on, choose Apple menu > System Preferences, click Startup Disk, and then click Target Disk Mode.
When the computer has started up, a disk icon appears on the desktop of the other computer.
Transfer files by dragging them to and from the disk.
Eject the disk by dragging its icon to the Trash.
While you drag, the Trash icon changes to an Eject icon.
On the computer you used as a disk, push the power button to shut it down, and then disconnect the cable.
Source: Apple KB - https://support.apple.com/kb/PH10725
Best Answer
No Mac will boot to an OS older than itself, with the exception of models released right on the cusp of a new major OS version.
The drivers for the newer model didn't yet exist.