iMac EFI Firmware Update 1.4

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:

IM91.008D.B08

For detailed information on this update, please visit this  website.