See the Technical Specifications for the full list of requirements. The latest supported software version is noted next to each model. You can install Mac OS X Lion on any of these Macs. Mac OS X Snow Leopard 10.6.6 or later or Mac OS X Lion 10.7 already installed.The same practice was also applied to its predecessor, Mac OS X Lion.Mac OS X Lion 10.7 is available for older systems that are not compatible with the latest version of macOS.

Apple later allowed free downloads of the OS, especially for customers of older and no longer officially supported Macintosh computers, starting on June 30, 2021. Mountain Lion was the last paid upgrade for an OS X major release, with OS X Mavericks and later being free. Mountain Lion sold three million units in the first four days, and has sold 28 million units as of June 10, 2013, making it Apple's most popular OS X release. OS X Mountain Lion received positive reviews, with critics praising Notification Center, Messages, and speed improvements over Mac OS X Lion, while criticizing iCloud for unreliability and Game Center for lack of games. It was released as a downloadable update later. Facebook integration was also planned but unfinished at launch date. Integrated links allowing the user to rapidly transfer content to Twitter were present in the operating system from launch. Mountain Lion also added a version of iOS's Notification Center, which groups updates from different applications in one place. As on iOS, Notes and Reminders became full applications, separate from Mail and Calendar, while the iChat application was replaced with a version of iOS's Messages. The operating system gained the new malware-blocking system Gatekeeper and integration with Apple's online Game Center and iCloud services, while the Safari web browser was updated to version 6.

Games for mac os x 10.7