The System BIOS

 

Basic functions

 

The BIOS performs the following boot functions in a typical computer system:

 

- Takes inventory of all hardware in the system and checks to ensure each components' basic operability.

- Recognizes and configures new hardware such as hard drives and floppy drives.

- Locates a valid OS and transfers the control of the system to that OS after boot functions have completed.

 

The BIOS also performs the following tasks during the normal operation of the system:

 

- Interacts with the OS to configure hardware behavior.

- Enables and disables integrated devices.

- Interacts with the 'hardware abstraction' layer to ensure compatibility between newer hardware and older applications.

- Affects system power properties.

- Provides a level of system security.

 

Post (Power On Self Test)

 

- When the computer first turns on, a POST is performed to ensure that all critical devices are operating.

- Devices checked include memory, drives, cpu, system timer, chipset, all peripheral cards, and memory.

- When all devices are deemed operable, the BIOS passes system control over to the OS.

- If a device is malfunctioning, and error code is generated in the form of beep codes and/or text.

- During POST, the system BIOS reads peripheral BIOS routines and runs them (see below).

 

The Peripheral BIOS

 

- Each installed device has its own 'BIOS'. This 'peripheral BIOS' interacts with the system BIOS.

- It is the peripheral BIOS which identifies the device to the system BIOS and the OS.

- This is how the OS determines if it has a driver for the device when the device is first installed.

 

Example: When the computer is turned on, the system BIOS looks first to the video BIOS. The video BIOS identifies itself and initiates the video capabilities. This is why you often see the identifying video adapter information before you see system information on power-up.

 

CMOS

 

Complimentary Metal Oxide Semiconductor. Pronouced “SEE – Moss”

The physical semiconductor used to carry the subroutines that run the BIOS

CMOS uses a complimentary arrangement of both NMOS and PMOS, negative and positive Metal Oxide transistor circuits.  CMOS memory draws very little current (nano-Amps). Values stored in it can be maintained for very a long period of time while the computer is off with a rechargeable lithium battery.  The CMOS memory is used to store system configuration information, such as disk drive parameters, memory configuration, and the date-time, some of which you enter in the CMOS Setup program, .  It is used by the Basic Input Output System (BIOS), a program permanently stored in the flash memory on recent motherboards and in read-only memory (ROM) on older motherboards, to configure the computer. The CMOS Setup is part of the BIOS program. The CMOS memory is usually located with the real-time clock in the motherboard chipset or in a separate real-time clock chip.  It is located in the chipset on most recent motherboards.

 

Setup

 

- The actual parameters and system settings that can be configured.

- Accessed on startup. Method of access depends on vendor.

 

Examples: Dell: press the f2 or 'delete' key; Compaq: press f10; Gateway: press F1

Generally the industry is becoming more uniform with entering setup Laptops are usually F2 and Desk tops are usually F1 or DEL

Older Gateways and Acer could be CTRL + ALT + ESC

 

The Battery

 

The BIOS is powered by a battery that retains the data when the system is off.

Modern BIOS batteries are standard NiCad batteries

Types of CMOS batteries - The following is a listing of the types of batteries found in computer to power the CMOS memory. The most common type of battery is the Coin cell battery (Lithium Battery)  the coin cell battery is the size of a dime, as shown below.

 

Life time of a CMOS battery - The standard life time of a CMOS battery is around 3 to 7 Years, however this amount of time can change depending on the use and environment that the Computer resides. If the Computer has been without power for and extended period of time (anywhere from a few weeks to months) it can greatly reduce the batteries life span.

Week Batteries can cause  illegal operations, loss of peripherals settings, clock setting and bad reloads of operating systems, for a few examples.