Apple has released iMac Hard Drive Firmware Update 1.0 for 21.5-inch and 27-inch iMacs that debuted in mid-2010. The update addresses an issue that was prevents some computers from booting properly.
It’s a 767KB download and requires Mac OS X 10.6.7. You can obtain it here (http://support.apple.com/kb/DL1378) or via the Software Updates component of the Mac OS X Systems Preferences app.
