Mac OS Startup Key combinations for Intel-Macs

Keystroke	Description
Press C during startup	Start up from a bootable CD or DVD, such as the Mac OS X Install disc that came with the computer.
Press D during startup	Start up in Apple Hardware Test (AHT), if the Install DVD 1 is in the computer.
Press Option-Command-P-R until you hear two beeps.	Reset NVRAM
Press Option during startup	Starts into Startup Manager, where you can select a Mac OS X volume to start from. Note: Press N to make the the first bootable Network volume appear as well.
Press Eject, F12, or hold the mouse (/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 FireWire 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.