Apple has updated Boot Camp, software included with Mac OS X that lets you run compatible versions of Windows on an Intel-based Mac. The upgrade adds support for 64-bit versions of Windows 7 and Windows 8.
The Boot Camp update is available in two versions. Version 5.1.5640 is mid-2013 MacBook Airs, late-2013 MacBook Pro with Retina display models and late-2013 iMacs. Version 5.1.5621 (http://support.apple.com/kb/DL1720) is available for a variety of other Mac models. Both are free downloads from the Mac App Store.