On the screen and behind the scenes, Apple’s new desktop operating system, OS X Yosemite, is packed with new features large and small. From a graphical overhaul that even changes the Mac’s longstanding fonts to reconfigured apps that sling data back and forth from your computer to your iDevice, it’s a big leap for Apple. Here’s what you need to know before you download Yosemite: Who Can Use It: This rule isn’t confirmed by Apple, but if your Mac’s body is made of aluminum, it can probably run Yosemite.