Mainboard

The most important thing to remember about the motherboard is that it is a printed circuit board which provides all the connections, pathways and "lines" connecting the different components of the computer to each other - specifically, the Central Processing Unit or CPU, which is where (as its name implies) all the "processing" is going on to everything else.

The CPU or "chip" (the most popular of which is Intel's pentium series) is an assembly of transistors and other devices (Pentium IV has over 4 million transistors) which perform or processes myriad programmed tasks.

The CPU rests in a "socket" on the motherboard which is connected to the other components through the board's printed circuits. The most important connections are to the chipsets - especially the northbridge chipset which is connected to the main computer memory (hard disk and RAM), while the southbridge set is connected to the peripherals - video and audio cards, IDE controllers, etc.

Aside from these, the most important element of the motherboard is the BIOS chip - which performs key functions like checking power supply, the hard disk drive, operating system, etc. before the computer actually starts "booting up". Turning on the computer automatically starts the BIOS chip up to perform its diagnostic functions, after which it powers up the CPU which - in its turn - starts powering up the other peripherals (hard disk, operating system, video and audio, etc.).

This is why the motherboard is the key component of the computer. It is, in effect, the "housing" for the CPU - the place where the latter resides and from which commands, instructions, and power course through before being sent out to other components.

Source : http://wiki.answers.com/Q/FAQ/4320