What exactly it is... BIOS or CMOS?

In Summary:
BIOS - Basic Input/Output System
CMOS – Complimentary Metal Oxide Semiconductor
Bios is a firmware chip that holds the instructions to control low level hardware.
Unlike BIOS, the CMOS is a read/write chip, which means users can save settings to the chip.
BIOS uses Read-only Memory (ROM)
CMOS uses Random Access Memory (RAM)
The BIOS and CMOS chips work hand-in-hand. BIOS has the basic instructions and CMOS has the instructions which users can change. For example the system time, boot priority/order, CPU clock speed, or the CPU multiplier.
BIOS instructions are flashed to the chip where as CMOS settings need to be saved in memory. This is why the CMOS has a battery. The bettery gives power to the system to allow the information to be saved and stored to the memory.
The locations of the chips can be anywhere on the motherboard, however generally they are on the bottom right hand side. Usually the CMOS chip will be located close to the CMOS battery. Next to the battery will be a reset jumper which allows resetting the CMOS to factory default settings.
While the BIOS settings are constant the CMOS setting are volatile. This means if the reset jumper is removed or if the system looses power by the battery being removed the CMOS settings will be lost.
While original equipment manufacturers (OEM) have differing firmware there are many simularities in the CMOS setup screens.

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