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A firmware update is installed using different steps. When you see the update in Software Update, it downloads a small utility that puts the firmware files onto the EFI partition of the hard drive (a hidden partition), so during the next startup, your Mac will start beeping and it will install the firmware update. When it finishes, your Mac will restart and the firmware update will be installed.
As you are having problems with the download from Software Update, I recommend you to download the installer from the Apple site, and follow these steps to install the firmware update. Disconnect everything you have connected to the Mac and make sure that you have your computer connected to a power source during the update
Sorry, I did not mention that I did download the software from the Apple Downloads site.
I am still confused:
1) according to the Library/Receipts/InstallHistory.plist the software was installed (I certainly ran the installation package);
2) there is no evidence of an installer in the Applications/Utilities folder. This at least implies that the firmware update did take place (I have rebooted since yesterday).
Is there a way to check if the firmware was updated? If it hasn't been, would there be any possible problem if I download the installer again? If it has been installed, then the problem remains as to why the software still appears in the software update.
It's possible that the update was installed, but the SMC ROM wasn't updated, so the package was installed on OS X but the ROM hasn't been updated. In order to check if you are running the latest SMC version, see > http://support.apple.com/kb/ht1237
I recommend you to download the installer again and follow the steps again
I had the same problem. Tried all the proposed fixes. Nothing worked. This solved my problem:
1. Install a fresh copy of mountain lion on an extern disk
2. Startup from that disk
3. Update to 10.8.3.
5. Open app store, go to updates. You should see the SMC 1.1. update.
6. Click update
Once the update installed (fan will go quickly to max speed during startup) switch back to your internal disk and start up. Now the SMC 1.1. update shouldn't show up in the app store/upadtes.