Apple released 27-inch iMac Firmware Update 1.0 late on Monday to address display flickering issues. This marks Apple's second attempt to correct display issues in the 27-inch iMac though firmare updates.
The company previously issued a firmware update in December 2009 that targeted the ATI Radeon HD 4670 and 4850 video cards used in the big screen iMac. That update was called 27-inch iMac Graphics Firmware Update 1.0, and is required before installing the new firmware update.
27-inch iMac Firmware Update is available via Apple's Software Update application, or as a download at the Apple Support Web site.