You can use the following startup key combinations with Intel-based Macs.
|Press C during startup
||Start up from a bootable CD, DVD, or USB thumb drive (such as OS X install media).
|Press D during startup
||Start up in Apple Hardware Test (AHT).
|Press Option-Command-P-R until you hear startup sound a second time.
|Press Option during startup
||Start up in Startup Manager, where you can select an OS X volume or network volume to start from.
|Press Eject, F12, or hold the mouse or trackpad button
||Ejects any removable media, such as an optical disc.
|Press N during startup
||Attempt to start up from a compatible network server (NetBoot).
|Press T during startup
||Start up in Target Disk Mode.
|Press Shift during startup
||Start up in Safe Boot mode and temporarily disable login items.
|Press Command-V during startup
||Start up in Verbose mode.
|Press Command-S during startup
||Start up in Single-User mode.
|Press Option-N during startup
||Start from a NetBoot server using the default boot image.
|Press Command-R during startup
Start from the OS X Recovery System1
1 Available on Macs that ship with OS X Lion. Some CPUs require an EFI BootROM update to support this feature.
For the best experience with startup keys, press the keys immediately after the startup tone plays.