If you look on the right of: http://support.apple.com/kb/DL1444 it says "related articles." One of them is " ■Intel-based iMac: Installing available updates," Clicking on that reveals the reason. The firmware update is only for 2011 iMacs:
Your 2009 iMac is supported only by two special updates:
If neither of those fixes your problem, and you don't have AppleCare, the cost of fixing your internal hardware issues that are not RAM related probably isn't worth it, unless an Exchange/repair program is issued for your Mac on this page:
You can always post to http://www.apple.com/feedback/ if you feel your model has been left out of the loop of those programs. Or if you want try to troubleshoot here what went wrong.
I agree though it was difficult to notice which machine it was for, if you happened to come upon the update either via Software Update or via a search engine on the net. I've requested the authors of the articles be more specific on the DL pages which vintage Macs are able to take certain updates if they are limited to specific vintages. You can do the same: http://www.apple.com/support/feedback/
One thing to remember, if you ever had a logicboard replacement, or you bought new or refurbished and don't know the history of the logicboard, that could be an indication that the firmware update may not apply. Of course if you are having system problems that would indicate a logicboard problem, you should bring it in for service anyway. If you want to isolate a hardware versus a software problem:
1. Backup your data at least to two physical sets of media. (I.e. two hard drives, or a hard drive and DVDs, etc... depending on your tolerance for waiting for recovery).
2. Run the hardware test that came with your machine:
- If the hardware test shows no problems, and your hard disk is not over 85% full, you may just need to repair the directory as indicated here*:
- If repairing the directory doesn't solve the problem, and you aren't using any tools like Onyx, MacKeeper, Macaroni, Antivirus, non-Apple Firewall software,
and the system is non-responsive to command-option-escape when it is busy, or you are getting four language screens you must restart now with no-non-Apple peripherals attached, then you likely have either a RAM problem or a hardware problem that can't be isolated elsewhere and need to bring it in for service. It is more likely a hardware problem if booted off CD you get the error message, and the disc is definitely for that Mac, or a supported newer retail operating system.