BIOS is short for Basic Input-Output System. The BIOS is actually software that is stored on a ROM chip on the motherboard. Most systems today use a Flash EPROM (Erasable Programmable ROM) to store the BIOS so that the user can update the programming code in the BIOS.
The BIOS is responsible for controlling or managing low-level but extremely important processes like the POST (Power-On Self-Test), the boot process, and the interaction of components on the motherboard.
CMOS is short for Complementary Metal-Oxide Semiconductor, which is the type of manufacturing process that creates most integrated circuits. This development process is used to create the following:
- High-density DRAM (Dynamic Random Access Memory)
- High-speed processors
- Low-power devices for mobile use
The term complementary refers to the fact that these chips use negatively and positively charged transistors (which complement each other) to store information. Most RAM chips rely on CMOS technology to store information, but when discussing CMOS, you will probably be referring to the hardware configuration settings that are saved between reboots of your computer.
These settings include
- Which hard drives and floppy drives are present?
- How much memory is installed?
- Is a keyboard required to boot?
- What type of mouse is installed (PS/2 or serial)?
- What are the reserved resources (such as IRQ, I/O addresses, and DMA channels)?
- What is the power-on password and is it required to boot up the system?
- What are the date and time?
- Is ACPI (Advance Configuration Power Interface) enabled, and what devices does it apply to?
Remember that BIOS stores programming code, and CMOS stores settings for the BIOS options.