Mike Meyers’ A+ Guide to Managing and Troubleshooting PCs Instructor’s Manual
Chapter 5
Chapter 5
BIOS and CMOS
Learning Objectives
In this lesson, you will learn how to identify various BIOS types, understand how the BIOS functions,
configure the CMOS setup utility options, describe the BIOS device drivers, and troubleshoot POST and
CMOS. By the end of this lesson you should be able to do the following:

Explain the function of BIOS

Describe BIOS and device drivers

Distinguish among various CMOS setup utility options

Troubleshoot the Power-On Self Test (POST)
Pre-test
1.
Describe the function of the basic input/output services (BIOS).
2.
Describe the function of the complementary metal-oxide semiconductor (CMOS).
3.
The desktop clock losing time is a symptom of what?
4.
Name a common method to enter the setup program.
5.
What is it called when you update the BIOS?
Lecture Outline
Historical/Conceptual
I.
We Need to Talk
A. Two functions are necessary for devices to work:
1.
CPU must have a way to talk to devices.
2.
Devices must have a way to send data to and receive data from the CPU.
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B. Northbridge, the first chip in the chipset, connects the CPU to video and/or memory.
C. Southbridge, the second chipset chip, handles all inputs and outputs to the many devices in the
PC and extends data bus and address bus to all other parts of PC.
D. Basic input/output system (BIOS) holds the programming code that allows the CPU to
communicate with the rest of the system.
1.
BIOS held in read-only memory (ROM).
E. Talking to the keyboard
1.
Example: how the CPU recognizes when a key is pressed.
a)
A keyboard controller chip (now part of the Southbridge) recognizes when a key is
pressed. Let’s say the A was pressed.
b) The keyboard controller reads the data and looks it up in its “code book” to determine
what key is pressed.
c)
The keyboard controller then gets the attention of the CPU, essentially saying, “I have
some data.”
d) When the CPU addresses the keyboard controller, the keyboard controller places the
data onto the external data bus so that the CPU can read it.
e)
For all of this to work, programming has to be readily available to the CPU and the
keyboard controller as soon as it is powered up. This programming is stored in ROM.
Discussion Point
Putting it together
In the first few chapters, various components were discussed, including address buses, data
buses, RAM, CPUs, chipsets, support chips, caches, input devices, storage devices,
and output devices. The BIOS is simply a group of programs stored in a secure place (a
ROM chip) that serves as the basic instruction code to control all that hardware.
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F.
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Read-only memory (ROM) chip also called system ROM or the ROM BIOS.
1.
Non-volatile (does not lose its programming, even if no power)
2.
Read-only means it cannot be easily erased
3.
Stores hundreds of programs referred to as basic input/output services (BIOS)
4.
ROM BIOS typically holds 64KB (65,536) lines of data code, though current Flash ROM
is often 2MB or more in size
5.
Historically a DIPP chip with a shiny label on it, but has gone through many changes
E. Each time the CPU needs to talk to a component, it refers to the BIOS for the program to talk to
that specific device.
F.
The CPU talks to the ROM BIOS the same way it talks to RAM—through the address bus—
with some of the address bus being reserved for the ROM BIOS.
G. Many devices and expansion cards have their communication programs on ROM chips.
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. Compare this to devices and chips
that you can physically touch, which is referred to as hardware.
Essentials
II. Complementary metal-oxide semiconductor (CMOS)
A. What it is
1.
A separate chip from the ROM BIOS
2.
Volatile: kept alive by a battery
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3.
Also acts as a clock and keeps the date and time
4.
Stores only the changeable data, not programs, read by the BIOS
5.
Customizable via setup program. Setup program is stored on the ROM BIOS, but the
customizable settings are on the CMOS chip
6.
Stores semi-permanent, user-changeable data related to hardware components such as disk
drives, RAM, and I/O ports
7.
Is typically 64 KB, but only a fraction of that is actually used to store the critical data
III. CMOS Setup Utilities
Discussion Point
BIOS manufacturers
In 1998, Phoenix and Award merged as Phoenix. However, Phoenix still markets Phoenix and
Award BIOS separately.
A. Updating CMOS: The Setup program
1.
The CMOS setup program is built into the system ROM chip and may be accessed in a
number of ways, depending on the manufacturer and date of the ROM chip.
a)
Many BIOS manufacturers. Each manufacturer uses a different key sequence to enter
the CMOS setup and may use a different key sequence within different models of the
same brand.
b) The most common BIOS manufacturers and some common key sequences to enter the
CMOS Setup (usually says on the boot screen) are
(1) Award (most common): Press DEL
(2) Phoenix: Press CTRL-ALT-ESC or F2
(3) American Megatrends (AMI): Press DEL
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(4) For others press F1, CTRL-ALT-INS, CTRL-ALT-ENTER, or CTRL-ALT-S
B. A quick tour of a typical CMOS setup (Award)
1.
CPU soft menu: Found on newer “jumperless” motherboards; controls things like voltages
and multipliers. Normally, you would keep these settings at AUTO.
2.
Advanced BIOS settings: Boot option, as well as other miscellaneous items usually found
here.
3.
Advanced chipset features: Deals with low-level chipset functions. Normally, you would
leave settings here at their default values.
4.
Integrated peripherals: Used to configure ports.
5.
Power management: Used to set sleep timers method. Also often used to configure IRQs
(Enabled/Disabled/AUTO).
6.
PnP/PCI configuration: Set up plug-and-play configurations and also sometimes IRQ
settings.
7.
PC Health Status.
8.
Set Password: Set user password (a password to boot the computer) or an administrator
password (to get into CMOS).
9.
EXIT: Save or not save the changes made to the CMOS.
Discussion Point
CMOS options
A typical CMOS setup has tons of options you can adjust. Few techs, if any, know what they
all mean. Basically, if it is not covered in the text, it is probably not critical to the PC
function and it probably is not on the CompTIA A+ Certification exam. Leaving those
settings at their default values is usually fine.
Discussion Point
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Modern CMOS
In the newer version of motherboards, the CMOS chip is being phased out. Since the advent
of Flash ROM, the PROM chip now has the ability to store the CMOS data within itself,
eliminating the need for a separate CMOS chip.
IV. Option ROM and Device Drivers
A. Option ROM or Bring your own BIOS (BYOB)
1.
Individual ROM BIOS on expansion cards and devices
2.
Device drivers loaded into RAM at boot
B. Device drivers—file stored on the hard drive that loads all the BIOS commands for a specific
device into RAM at boot
1.
Comes with a device you buy as an installation discs (floppy or CD-ROM)
C. BIOS, BIOS, everywhere
1.
Every piece of hardware must have a program that allows the CPU to communicate with it.
a)
Program may be on motherboard ROM
b) Program may be on ROM on the individual hardware
c)
Program may be on a driver
d) Program may be loaded into RAM at boot
IT Technician
V. Power-On Self Test (POST)
A. Upon boot, the ROM initiates the POST process
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The POST routine sends out a message to all assumed components to initiate self tests.
This determines whether or not the components are working properly. Quality of POST
diagnostic determined by component.
2.
If a component fails self diagnostics, the POST process halts and sends an error message.
B. Before and during the video test: beep codes
1. If video is missing or faulty, you’ll hear one long beep followed by three short beeps.
2. If RAM is missing or faulty, you’ll hear a rather alarming buzzing that will repeat as
long as the computer is on.
3. If POST completes successfully, you’ll hear one or two short beeps.
C. Text errors
1.
Once the video is determined to be good, errors can be displayed.
2.
Errors are usually displayed in clear text, though they can sometimes be rather cryptic.
D. POST cards
1.
The small expansion card installs into an available slot.
2.
Note the light emitting diode (LED) display to see what device POST is currently checking.
Refer to the two-digit hex code on the LED display to determine the faulty POST code.
3.
Look up the code in the companion manual. It can help identify the faulty component.
4.
If the PC passes POST, the problem is more likely a software problem.
Discussion Point
Beep codes and POST codes
Each BIOS manufacturer sets the beep codes to its own internal needs. Different versions of
BIOS from the same manufacturer can have different beep codes. The same thing
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goes for POST codes when using a POST card. Each BIOS version responds with a
different two-digit hex code for a specific error.
Discussion Point
Diagnostic tip
If you are receiving intermittent beep codes or POST codes, try turning the power on and off
several times and see if the same code comes up each time. If it is not the same code
each time, the problem might be the power supply.
E. The boot process
1.
CPU “wakes up” and checks for proper voltage. If proper voltage is found, CPU sends a
built-in memory address, which is the first line of the POST program on the system ROM.
2.
The ROM begins the POST routines.
3.
Once POST is passed, the ROM begins the boot process (the bootstrap loader) by looking
for an operating system according to the CMOS settings.
4.
The CMOS settings tell it which device to try to boot from. It looks at the boot sector of
that device (floppy, CD-ROM, hard drive, etc.) and tries to load an operating system.
5.
Once the boot process begins, control is handed over to the operating system.
VI. Care and feeding of BIOS and CMOS.
A. Losing CMOS settings
1.
Battery provides continuous trickle charge to hold data. Also keeps clock running
2.
If battery dies or is removed, all data is lost and system returns to factory defaults
3.
Common errors
a)
CMOS configuration mismatch
b) CMOS date/time not set
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No boot device available
d) CMOS battery state low
4.
Common reasons for losing CMOS data
a)
Pulling and inserting cards
b) Touching the motherboard
c)
Dropping something on the motherboard
d) Dirt on the motherboard
e)
Faulty power supplies
f)
Electrical surges
g) Chip creep
Discussion Point
Chip/board creep
PCs repeatedly get hot and cold, causing components to expand and contract regularly. Chips
that are just plugged into a socket can work their way out of socket due to this process.
Most chips today are soldered in to prevent this problem.
A similar concept is board creep. Due to the same hot and cold, expansion and
contraction, boards that are not secured in their slots will slowly work their way out.
5.
If settings keep resetting, replace the battery
B. Clearing CMOS
1.
CMOS has a failsafe on the motherboard. If you need to clear it to factor settings, use the
jumper or shunt to send a reset single to the CMOS.
2.
Useful if overzealous tech has changed one thing too many without normalizing.
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Useful if overzealous user has password protected the BIOS but forgot the password.
C. Flashing ROM
1.
Flash ROM chips can be reprogrammed.
2.
Download the program from manufacturer and follow instructions.
3.
Typically load onto floppy and boot from floppy.
4.
Only flash the BIOS if necessary.
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