by Tom Nelson
With the introduction of OS X Lion, Apple made fundamental changes to how OS X is sold and distributed. Install DVDs are history; OS X is now available as a download from the Mac App Store.
Screen shot © Coyote Moon, Inc.
With the elimination of install DVDs, Apple needed to provide alternative methods for installing the OS, repairing startup drives and system files, and reinstalling the OS. All of these capabilities were formerly available on the install DVDs.
Apple’s solution was to have the OS X download contain an installer that not only installs the OS on your Mac, but also creates a hidden volume on your startup drive called Recovery HD. This hidden volume contains a minimal version of OS X that’s enough to allow your Mac to boot; it also contains various utilities.