This update is recommended for iMac (late 2013) models. This update addresses an issue which may cause a black screen to appear when installing Windows 7 or Windows 8 using Boot Camp Assistant if both an external optical drive and USB thumb drive are connected to the system. This update also ensures that the system will boot by default into OS X after installation of Windows 8.
System Requirements: OS X Mountain Lion v10.8.4 (12E4022) or later
You can download the update from here: http://support.apple.com/kb/DL1684
Technical Support MVP
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