OS X Mountain Lion

OS X Mountain Lion, or OS X 10.8, is the ninth major release of the OS X operating system released on 25 July 2012. It introduced various revamps to the Lion user interface and fixed many of the paradigms that were found to be controversial in Lion. A new feature to OS X, Gatekeeper, prevents unsigned code from running on a Mac by default (in an attempt to prevent malware), although it can be disabled. A system-wide notification system has also been ported from iOS, known as Notification Center.

It is the first version to be released under the OS X name. It is also the first version to be released under the new annual release schedule for the operating system in which newer versions of OS X will be released annually in order to be consistent with the release schedule for iOS. It is also the last version of OS X to be released as a paid upgrade as subsequent releases would be released as free upgrades starting with OS X Mavericks.

Like in iOS 11, this version of OS X is the first to drop support for 32-bit kernels and corresponding 32-bit EFI BootROM Macs. The decision to drop 32-bit architectures was made relatively late in the development process, as Beta 1 (12A128p) shipped with a 32-bit kernel. This version drops support for NVIDIA GeForce 6000/7000 Series, ATi Radeon X800/X1000 Series and Intel GMA 900/950/3150/X3100 (Mobile 965 Express Chipset Family) graphics cards.

Software Update was also moved to the App Store in this version of OS X. This change would last until macOS Mojave in which the update functionality of the operating system was moved back to System Preferences.