This System Preferences panel, formerly called Software Update, governs when and how your Mac auto-downloads new versions of software you’ve acquired from the App Store (Chapter 5).
Whenever Apple improves or fixes some piece of OS X or some Apple-branded program, the Mac can notify you, download the update, and install it into your system automatically. These updates may include new versions of programs like iPhoto and iMovie; drivers for newly released printers, scanners, cameras, and such; bug fixes and security patches; and so on.
These four checkboxes that govern the process:
Automatically check for updates. This is where you grant permission to your Mac to ping the mother ship periodically to see if there are updates available. Turn it off, and you’re stuck with today’s software versions forever.
Download newly available updates in the background. If you leave this option turned on, you’ll still be notified before anything gets installed, but you won’t have to wait for the downloading—the deed will already be done.
Install app updates. If you turn this off, you won’t get OS X updates as they come along—only updates to your apps.
It’s hard to think of a reason why you wouldn’t want the latest, most refined versions of your apps. But maybe you want to read online about some update online before installing it.
Install system data files and security updates. If you turn this off, you won’t automatically get OS X updates as they come along.
Automatically download apps purchased ...