Owners of 27-inch iMacs will want to fire up Software Update, as Apple on Wednesday released a pair of updates for its top-of-the-line consumer desktops: 27-inch iMac EFI FW Update 1.0 and 27-inch iMac SMC Firmware Update 1.0.
The 2.1MB EFI update applies only to those users of 27-inch iMacs powered by the quad-core Intel Core i5 and Core i7 processors: it fixes a problem that caused the process to ramp up while playing audio through the headphone jack and corrects an issue that resulted in the display backlight not turning on when the iMac was powered on. It requires Mac OS X 10.6.3 or later.
The comparatively tiny 397KB SMC Firmware Update addresses compatibility issues with Target Display Mode - that's the feature that allows you to use an iMac as an external monitor. It also requires Mac OS X 10.6.3 or later.
Both updates are available from Apple's support downloads page as well as via Software Update.