This update fixes intermittent system freeze issues for iMac computers with ATI Radeon HD 4850 graphics and fixes wake-from-sleep issues in Boot Camp.
To complete the firmware update process, please follow the instructions in the updater application (/Applications/Utilities/iMac EFI Firmware Update.app). The updater will launch automatically when the Installer closes.
After the firmware is successfully applied to your Mac, your Boot ROM Version will be:
You can launch Software Update from the Apple Menu at the top left of your screen.