iMac ATI Radeon HD Graphics Firmware Update 1.0.1
It updates the ATI Radeon HD 2600 Pro or ATI Radeon HD 2400 XT graphics card firmware in the iMac to improve system stability.
To complete the firmware update process, please follow the instructions in the updater application (/Applications/Utilities/iMac ATI Radeon HD Graphics Firmware Update.app). The updater will launch automatically when the Installer closes.
After this update has been successfully completed, ROM version will be: 113-B2250L-259
For more information, visit:
http://www.apple.com/support/downloads/imacatiradeonhdgraphicsfirmwareupdate101.html

