Apple today released iMac Hard Drive Firmware Update 1.0, a new update to address issues with system booting on the company's current-generation "Mid-2010" iMac models.
About iMac Hard Drive Firmware Update 1.0
This firmware update fixes a hard drive issue that may prevent some iMac (21.5-inch and 27-inch, Mid 2010) systems from booting properly.
The update weighs in at 767 KB and requires Mac OS X 10.6.7.
Top Rated Comments
If it says you don't need it, you don't need it. It checks your hard drive model against the affected models. :)