OS X Mountain Lion (version 10.8) is the ninth major release of macOS, Apple Inc.' S desktop and server operating system for Macintosh computers. OS X Mountain Lion was released on July 25, 2012 for purchase and download through Apple's Mac App Store, as part of a switch to releasing OS X versions online and every year, rather than every two years or so. If you’re using macOS Mojave or later, choose Apple menu System Preferences, then click Software Update. If you’re using an earlier macOS, use the App Store instead. Learn how to download and install macOS Big Sur Go to the App Store.

Upgrade to macOS Big Sur

Before installing this upgrade, make sure that your Mac is ready.

Check compatibility

macOS Big Sur supports most Mac models introduced in 2013 and later.

Make a backup

Before you upgrade, make a complete backup with Time Machine, or store your files in iCloud.

Free up space

If the installer needs more storage space to upgrade, you can free up space using tools that come with your Mac.

Download macOS Big Sur

If you’re using macOS Mojave or later, choose Apple menu  > System Preferences, then click Software Update. If you’re using an earlier macOS, use the App Store instead.

Get to know macOS Big Sur

Learn about some of the new features of macOS Big Sur.

Control Center

Control Center brings favorite controls such as Bluetooth, Wi-Fi, Do Not Disturb, and Sound together in a single place—so you can easily adjust them at any time.

Notification Center

Notification Center puts notifications and>

Safari

Customize your start page, navigate with ease using the new tab bar, and access a new privacy report to see just how Safari protects your privacy as you browse.

Maps

Discover great places around the world and navigate easier with guides, cycling directions, indoor maps, Look Around, electric vehicle routing, and more.

Messages

Send messages to friends and family using new tools that make it easier to keep track of group conversations and give you fun, engaging ways to express yourself.

Photos

Use the expanded editing capabilities in Photos to easily make simple changes and more advanced adjustments to your photos.

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Mac Os Mojave Apple Store Link