1. Suleiman Mohammed (mcpn,mncs)
BIOS and CMOS
Instructor
Suleiman Mohammed (mcpn,mncs)
Institute of Computing & ICT, Ahmadu Bello University, Zaria.

2. Overview In this chapter, you will learn to
Explain the function of BIOS
Distinguish among various CMOS setup utility options
Describe option ROM and device drivers
Troubleshoot the power-on self test (POST)

3. Bridge Introduction Data flows through the computer
Between CPU and RAM
Between CPU and video
Between CPU and other devices
Bridges are used to connect the pieces
Northbridge
Bridge closest to the CPU
Southbridge
The farther bridge

4. Northbridge & Southbridge
A chipset is a set of Northbridge and Southbridge chips that work together
Northbridge
Chip or chips that connect the CPU to video and/or memory
Southbridge
Handles all of the inputs and outputs to the many devices in the PC
Chipset makers rarely use the terms “Northbridge” and “Southbridge” anymore, but because most modern chipsets consist of only two or three chips with basically the same functions, techs continue to use the terms.
Explored in more depth in Chapter 7

5. Data Flow
Northbridge and Southbridge have connectivity with all devices
Not the same in all systems

6. Chipset
Northbridge
Southbridge

7. Basic Input/Output System (BIOS)
Bridges connect the devices
But without a program, they don’t know how to communicate
A special kind of program is required to enable the CPU to talk to other devices
A Flash ROM chip stores these programs
These programs are collectively known as the basic input/output service (BIOS)
The ROM chip on the motherboard that holds the system BIOS is called the system ROM, or ROM BIOS.

8. Talking to the Keyboard
The keyboard talks to the external data bus
Uses the keyboard controller chip (8042)
The Southbridge chip handles the keyboard interface, acting as the keyboard controller chip among its many other functions. Manufacturers today choose a specific chipset, rather than an individual keyboard controller.

9. Keyboard controller chip
BIOS
Each program is called a service
Programs stored on Flash ROM chips are known as firmware
Programs stored on erasable media are called software
Keyboard controller chip
Discussion Point
Software and firmware
Programs that typically reside in RAM or on other erasable media are called “software,” while programs that reside in ROM are called “firmware.”

10. Essentials
CMOS

11. CMOS Separate chip from ROM BIOS Volatile (kept alive by battery)
Stores only changeable data
Not programs
Acts as clock to keep data current
Customizable via SETUP program
Often on Southbridge

12. BIOS vs. CMOS CMOS BIOS Data Programs
Volatile (kept alive with battery)
Changed via CMOS setup
Typically 128 K of data (though chip size is typically 64 K)
Often on Southbridge
BIOS
Programs
Non-volatile (stays same after power off)
Can be changed by “flashing”
Typically 64 K of programs (though Flash ROM is much bigger)
Often a separate chip

13. Updating CMOS Updated via BIOS program Three primary BIOS brands
American Megatrends (AMI), Award, Phoenix
To enter setup, press key combination (may be Del, ESC, F1, F2, CTRL-ALT-ESC, CTRL-ALT-INS, CTRL-ALT-Enter, or CTRL-S)
BIOS manufacturers
In 1998, Phoenix and Award merged as Phoenix. However, Phoenix still markets Phoenix and Award BIOS separately.

14. CMOS Setup Main menu Access to all submenus Note
Not all Award CMOS setups will have the same pages as those listed here.

15. Standard CMOS Features
Clock, hard drives, floppy drives

16. Soft Menu Setup
Normally set to Default or Auto for all

17. Advanced Features
POST, boot order

18. Power Management
Use to enable/disable power-saving features

19. PnP/PCI
Rarely need to manipulate on today’s PCs

20. Set Password Locks access to CMOS settings
Prevents non-techs from changing key settings

21. Option ROM and Device Drivers

22. BYOB Computer makers could not predict all the new types of hardware
Ways to bring your own BIOS (BYOB) were invented:
Option ROM is a BIOS chip embedded on the adapter card itself – (i.e., video cards)
Most new hardware devices use device drivers to tell the BIOS how to talk to the CPU
Most devices with onboard BIOS use it only for internal needs (internal function) and use a device driver to talk to the CPU

23. Device Drivers
A device driver is a file that contains the BIOS commands necessary to communicate with the devices they support
Loaded into RAM when the system boots
All devices come with their own device drivers
Device drivers have one big limitation—they don’t start until the operating system starts them. Some devices still use ROM BIOS to enable them to boot the system.

24. BIOS, BIOS, Everywhere
All hardware needs a program to allow CPU to communicate with it
Could be on motherboard ROM
Could be on PC card ROM
Could be loaded via a driver
Could be loaded into RAM at boot

25. Power-On Self Test (POST)
IT Technician
Power-On Self Test (POST)

26. Power-On Self Test (POST)
The power-on self test (POST) is a special program stored on the ROM chip
Initiated when the computer is turned on or is reset
Checks out the system every time the computer boots
Communicates errors
Beep codes
Text errors

27. Beep Codes
If video is determined to be missing or faulty
One long beep followed by three short beeps
If everything checks out
One or two short beeps
If RAM is missing or faulty
Buzzing noise that repeats until power turned off
More complicated beep codes may be found in legacy computers
Check motherboard manual for meaning

28. Text-Based Error Message

29. POST Cards
POST cards are devices that monitor POSTs and report on the hardware that may be causing problems
Turn the PC off, plug in the card, and reboot
POST error codes do not fix the computer – they just tell you where to look
If all else fails, replace the motherboard

30. The Boot Process
The CPU is the first component initialized when the computer is turned on
It reads a special wire called power good once the power supply provides the proper voltage to the CPU
Every CPU has a built-in memory address with the first line of the POST program on the system ROM

31. The Boot Process
The last BIOS function called by POST is the bootstrap loader
The bootstrap loader loads the operating system from the boot sector
Searches the floppy, CD-ROM, or the hard drive
Boot order set in CMOS
The bootstrap loader generates an error if it cannot find the boot sector on the bootable disk

32. Care and Feeding of CMOS/BIOS
Instructor Tip
Pogo once said “We have met the enemy and he is us.” English grammar aside, the real message is that we are often our own worst enemy. Working with BIOS and CMOS is a great example. It often works fine until we start changing things. A sound troubleshooting principle is to do only one thing at a time, and if it doesn’t resolve the problem, put it back the way it was. The tech that makes change after change without normalizing the system inserts new problems.

33. Losing CMOS Settings Common errors Common reasons for losing CMOS data
CMOS configuration mismatch
CMOS date/time not set
No boot device available
CMOS battery state low
Common reasons for losing CMOS data
Jiggling the battery while doing other work
Dirt on the motherboard
Electrical surges
Faulty power supplies
Chip creep

34. Loosing CMOS Settings If your system keeps resetting
Replace the battery
Common symptoms of low battery
Slow running clock
Clock resetting to January 1st

35. Clearing CMOS Settings
To clear the CMOS settings, place the shunt on the CMOS jumper
Resets to factory settings
Resets password

36. Flashing ROM Flash ROM chips can be reprogrammed
Download program from manufacturer
Copy program to floppy
Some programs will run within Windows
Boot to floppy and run program

37. Thank You