Mac OS X v10.6.7 Update for iMac (Early 2011) ...The Mac OS X 10.6.7 Update for iMac is recommended for all early 2011 iMac models. It includes general operating system fixes for Mac OS X Snow Leopard that enhance the stability, compatibility, performance, and security of your Mac, including fixes that:

• Improve the reliability of Back to My Mac
• Resolve an issue when transferring files to certain SMB servers
• Address various minor Mac App Store bugs
• Address minor FaceTime performance issues
• Address issues with graphics stability and 3D performance
• Improve external display compatibility
• Improve Thunderbolt device support