A Mac’s Recovery Mode is for more than just reinstalling Mac OS X. You’ll find many other useful troubleshooting utilities here — you can use these even if your Mac can’t boot normally.
To access Recovery Mode, restart your Mac and press and hold the Command + R keys during the boot-up process. This is one of several hidden startup options on a Mac.
-Reinstall Mac OS X
-Restore From a Time Machine Backup
-Browse the Web
-Manage Your Disks
-Choose the Default Startup Disk
-Add or Remove an EFI Firmware Password
-Use Network Tools to Troubleshoot Your Connection
-Open a Terminal
Read more about: 8 Mac System Features You Can Access in Recovery Mode
