Originally Posted by Speedma11229
If it's the first time your powering up your custom built rig, then you're probably installing your OS, so you would want to change your first boot device to your CD drive. Then once it's installed change the first boot device back to your hdd.
This, but mind explaining your question a bit more? There's a lot we could tell you but overall the bios is this,
"The BIOS software is built into the PC, and is the first code run by a PC when powered on ('boot firmware'). The primary function of the BIOS is to set up the hardware and load and start an operating system. When the PC starts up, the first job for the BIOS is to initialize and identify system devices such as the video display card, keyboard and mouse, hard disk drive, optical disc drive and other hardware. The BIOS then locates software held on a peripheral device (designated as a 'boot device'), such as a hard disk or a CD/DVD, and loads and executes that software, giving it control of the PC. This process is known as booting, or booting up, which is short for bootstrapping.
BIOS software is stored on a non-volatile ROM chip built into the system on the motherboard. The BIOS software is specifically designed to work with the particular type of system in question, including having a knowledge of the workings of various devices that make up the complementary chipset of the system. In modern computer systems, the BIOS chip's contents can be rewritten, allowing BIOS software to be upgraded."
Via Wiki; http://en.wikipedia.org/wiki/BIOS