You’ll also need 7GB data space and 2GB memory on your machine. If you’re looking to download Mac OS X Lion, you’ll need OS X Snow Leopard 10.6.6 or OS X Lion 10.7 (weird, right?) already installed. You’ll also need 2GB memory, and 8GB data storage. If you’re looking to download Mac OS X Mountain Lion, you’ll need at least OS X Snow Leopard, Lion 10.7, or Mountain Lion 10.8. If you head to the Mac OS X Lion Installer page or the Mac OS X Mountain Lion Installer page, you can drop in and download each operating system version for free.
You can still buy Mac OS X lion and Mac OS X Mountain Lion from the Apple store for approximately $20 each, but they’ve also been made available for free through Apple support documents.
Starting with Mac OS X 10.9 Mavericks, Apple started making updates to their operating system free for compatible devices.
