Late Friday, Apple released an additional beta of its forthcoming Mac OS X 10.6.5 update. Per World of Apple, the beta, labeled build 10H571, arrived 5 days after Apple released an internal “pre-release build.”

According to the release notes, developers who installed Thursday’s Mac OS X 10.6.6 beta will need to revert to 10.6.0-10.6.4 in order to install the latest 10.6.5 build. Focus areas for the build are: 3D Graphics, Printing, QuickTime, Time Machine and USB Devices.

The public release of Mac OS X 10.6.5, which is required to take full advantage of the soon-to-be-released iOS 4.2, is expected to come soon.

The iOS 4.2 update is scheduled for a November release.