Mac OS X Lion: The Missing Manual

Startup Disks

When you turn the Mac on, it hunts for a startup disk—that is, a disk containing a System folder. If you’ve ever seen the dispiriting blinking folder icon on a Mac’s screen, you know what happens when the Mac can’t find a startup disk. It blinks like that forever, or until you find and insert a disk with a viable System folder on it.

Usually, a startup disk is a hard drive or a DVD. (Not all external USB disks are capable of starting up the Mac, but any internal hard drive can, and any external FireWire or Thunderbolt hard drive can.) You can even put a stripped-down, emergency copy of Lion onto a flash drive and start up your Mac that way; see Physical Recovery Disks.

UP TO SPEED: Mac OS Extended Formatting

Whether you use Disk Utility to erase a disk (or when you first install Mac OS X and elect to erase the hard drive in the process), you’ll be confronted with a choice between formatting options called Mac OS Extended and UNIX File System (UFS). (Depending on the kind of disk, you may also see an option to create a DOS-formatted disk for use in Windows machines.)

Mac OS Extended or Mac OS Extended (Journaled) refers to the HFS Plus filing system, a disk format that has been proudly maximizing disk space for Mac fans since Mac OS 8.1. (For a definition of journaling, see The Standard Installation.)

Mac OS X still accepts disks that were prepared using the older, Mac OS Standard formatting—the ancient HFS (hierarchical filing system) format—but you can’t use one as your ...