27-inch iMac EFI FW Update 1.0
The update is recommended for all quad-core Intel Core i5 and Core i7 processors 27-inch iMacs.
This update addresses the following:
- Resolves an issue that sometimes caused high processor utilization while playing audio through the headphone output mini-jack.
- Resolves an issue that prevented the display backlight from turning on after powering on the iMac.
When your computer restarts a gray screen will appear with a status bar to indicate the progress of the update. Do not disturb or shut off the power on your iMac during this update.
For more information about EFI firmware updates, please see this article: http://support.apple.com/kb/HT4125