When Mac boots, something wonderful would happen if you press some keys. Some keystrokes we use a lot, such as “Option” key, but some we rarely use and easily forget. Therefore, we get a collection and to find out what difference could these keystrokes bring for us. If possible, you may print these keys, and quickly refer to and solve problems for emergency.

When Mac boots, if you press:
C   boot your computer from CD or DVD, generally it’s used when reinstall or recover system, or do iDefrag operation.
D   If your Mac Installation CD/DVD is in CD-ROM/DVD-ROM, this key would let Mac inspect hardware.
N   Boot from network server. This function is available only when you’ve got only one server.
T   This key would be very useful, which could boot with target disk mode, when you connect two Mac laptops with a front line, press this Key and start your laptop, then it would turn to a big hard disk completely. And through another computer, you could do some operations to it like data recovery , disk copy and repartition. And sometimes, when your Mac could not install with CD (such as isntallation version is incorrect), with another computer, you could reinstall system easily.
Option   It would call boot manager, you oculd choose to boot from which system, and those guys who used BootCamp almost all know it. With this key, you could also choose to boot from CD-ROM/DVD-ROM, the replacement of key C
Option and then N    this function is similar to Option’s, t