Download Firmware Apple iMac EFI 1.4

Apple has released a firmware update for iMac computers equipped with a Radeon HD 4850 GPU. The update increases the version number of the Extensible Firmware Interface to 1.4 and can here downloaded as a dmg file. The new EFI version fixes freeze issues related to the HD 4850 graphics card and also brings improved Boot Camp support. The release notes of iMac EFI Firmware Update 1.4 are as follows:

About 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