Suleiman Mohammed (mcpn,mncs)
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Transcript of Suleiman Mohammed (mcpn,mncs)
Suleiman Mohammed (mcpn,mncs)
BIOS and CMOS Instructor Suleiman Mohammed (mcpn,mncs) Institute of
Computing & ICT, Ahmadu Bello University, Zaria. 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) 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 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 Data Flow Northbridge and Southbridge have
connectivity with all devices Not the same in all systems Chipset
Northbridge Southbridge Basic Input/Output System (BIOS)
Bridges connect the devices But without a program, they dont 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.
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. 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. Essentials CMOS 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 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 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.
CMOS Setup Main menu Access to all submenus Note
Not all Award CMOS setups will have the same pages as those listed
here. Standard CMOS Features
Clock, hard drives, floppy drives Soft Menu Setup Normally set to
Default or Auto for all Advanced Features POST, boot order Power
Management Use to enable/disable power-saving features PnP/PCI
Rarely need to manipulate on todays PCs Set Password Locks access
to CMOS settings
Prevents non-techs from changing key settings Option ROM and Device
Drivers 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 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 limitationthey
dont start until the operating system starts them. Some devices
still use ROM BIOS to enable them to boot the system. 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 Power-On
Self Test (POST)
IT Technician Power-On Self Test (POST) 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 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 Text-Based Error Message 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
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 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 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 doesnt resolve the problem, put it back the way it was. The tech
that makes change after change without normalizing the system
inserts new problems. 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
Loosing CMOS Settings If your system keeps resetting
Replace the battery Common symptoms of low battery Slow running
clock Clock resetting to January 1st Clearing CMOS Settings
To clear the CMOS settings, place the shunt on the CMOS jumper
Resets to factory settings Resets password 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
Thank You