You may notice a firmware, display, or dvd update for iMac Intels. Some do not list the vintage Mac they are compatible with. Until all do, it is highly recommended you check this listing first before attempting to download the update:
As with all updates, backing up your data first is not an option. It is required for the safety of your data.
If unsure which vintage your iMac is, ask in the forum for guidance, or check this data out:
Note, if your iMac looks like , it could be Intel, or it could be PowerPC G5. To tell the difference, shut it down, and tilt it over so the base is facing you. On the base is a label with an EMC#. If it is 2104, 2105, 2110, 2114, 2118, 2111, 2133, or 2134 it is Intel. Otherwise, it is PowerPC G5, and does not take any of the updates above.