BIOS and CMOSBIOS and CMOS

Instructor:Instructor:

Suleiman Mohammed(mcpn, Suleiman Mohammed(mcpn, mncs)mncs)Institute of Computing & ICT, Ahmadu Bello University, Zaria.Institute of Computing & ICT, Ahmadu Bello University, Zaria.

The CPUThe CPU

The CPU needs some method to talk to the devices to tell them what to do

The devices need some way to send data to, and receive data from the CPU

We need to expand our logical model from the CPU chapter

CPUNorthbridge RAM

EDB

Address Bus

CPUNorthbridge RAM

EDB

Address Bus

Southbridge

keyboard

Hard Disk Drive

Video Card

CPUNorthbridge RAM

EDB

Address Bus

Southbridge

KeyboardController

Hard Disk DriveVideo Card

Chipset

Chipset

845 Chipset

925 Chipset

KeyboardKeyboardHow we communicate with the keyboard

ProblemsProblems

Different motherboards have different keyboard controllers

We need specific code to talk to the controllerWe need a place to store this specific

programming and the programming for other devices (optical drive, floppy, etc.)

SolutionSolution

Use a ROM chipDoes not “forget” when power is removed,

like RAM doesSpecific to motherboard and devices on itRead only, code does not changeCan hold lots of programs, like a “chapter

book”Called “firmware”

BIOBIOS

IBM’s BIOSIBM’s BIOS

Patent “fence” around BIOS

Making a ROM chipMaking a ROM chip

We “burn” the code into the chip:

1 0

System ROMSystem ROM

Holds all the support programming for basic devices

Is given a specific address space, or range of memory addresses for its code

The First MegabyteThe First Megabyte

Upper Memory

Conventional Memory

Address 0

640 KB

1 MB

(384 KB)

Basic HardwareBasic Hardware

CPUMouseKeyboardVideo cardRAMNetwork card

Sound CardFloppy driveHard Disk driveZip driveUSB portsCD-ROM drive

Basic HardwareBasic Hardware

• CPU• Mouse• Keyboard• Video card• RAM• Network card

• Sound Card• Floppy drive• Hard Disk drive• Zip drive• USB ports• CD-ROM drive

Stored InformationStored Information

Stores access/write code for keyboardStores access/write code for system speakerStores access/write code for other chips

(functions) on motherboardDoes not change (more on this in a moment)

CMOSCMOS

Complimentary Metal Oxide Semiconductor – how it was made

Stores specific information about your system: Amount of RAM present Type of hard disk drive Date and Time

Needs battery power to “remember” when power is off

CPUNorthbridge RAM

EDB

Address Bus

Southbridge

KeyboardController

Mouse Video Card

Chipset

BIOSAndCMOS

Chipset

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BIOSBIOS

All devices need BIOS code to interoperate with CPU. Some is stored directly in System BIOS chip, most is stored elsewhere.

One of the functions of BIOS is to provide the CMOS Setup Utility, or Setup, which allows us to change CMOS data.

BIOS information CMOS

information

CMOS or SetupCMOS or Setup

Option to use this program is early in the boot cycle – long before system loads Operating System

Different key(s) to enter different SetupsYou should only get to Setup on purposeProgram stored in BIOS, but only edits data

in CMOSFirst CMOS was set of switches!

Who makes BIOS?Who makes BIOS?

Award SoftwarePhoenix TechnologiesAMI – American Megatrends Inc.They write BIOS with lots of options;

motherboard maker picks sections to be usedLong gone are IBM’s patents on BIOS

Same parent company

SetupSetup

Lots of screens and subscreensYou don’t need to know about all settings on

all screensMotherboard book is mildly helpful on some

optionsYou should know generally where things can

be found

Date and Time and …Date and Time and …

Usually on the first screen, or first menu choice

Lets you set Date, Time, floppy present (will autodetect it), memory count, hard drive(s) present (again, autodetected)

Here is where you set the boot

order

When adding a modem, you might want to turn both of

these off.

Old CMOSOld CMOS

Stored the hard drive “geometry” which was NOT found on the drive’s label

Old systems had a nasty habit of loosing CMOS data and requiring a trip to the repair shop to get fixed

I spent many an hour hacking drive geometry values by trial and error

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New CMOSNew CMOS

Did you notice the “High Performance” option?

Did you see the “Setup Defaults” option?BIOS can “talk” to hard disk drive and get all

the information it needs.About the worst that happens today is the

need to reset date and time.

Chip EvolutionChip Evolution

EPROM – Erasable Programmable ROM; used ultra-violet light (sunlight) to erase

EEPROM – Electrically Erasable – what we use today

Flash ROM – another name for EEPROMNVRAM – Non-volatile RAM. Really not so,

still needs battery power

The Three-In-OneThe Three-In-One

We have BIOS that stores code and access program to CMOS

We have CMOS that stores changeable information about our system

We have RTC (Real Time Clock) that keeps track of date and time

All three are now rolled into one chip

Easy way to spot this chip is by the

shinny label

About that BatteryAbout that Battery

Should last 5 to 10 yearsYou can find them at Savon evenIf your system forgets date and/or time, it’s

time to replace the batteryBeware the evil ESD!

More BatteryMore BatterySometimes we WANT to reset CMOS:

A forgotten password Too aggressive overclocking Incorrect low-level settings on some screen

Either move the jumper, or pull the batteryDo either for about 10 secondsIf you are to pull battery, make sure you

unplug system too

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More BIOSMore BIOS

Option ROM – put a BIOS chip on the card/device Video is most common for this SCSI cards Network cards have socket, chip is extra

Software SolutionsSoftware Solutions

Device Drivers – very flexible, but must wait until OS starts loading.

CONFIG.SYS – DOS utility program, runs before DOS really gets going

SYSTEM.INI – Introduced with Win 1 to 3, another text file. Win 9x won’t boot without it; XP will

The Registry – Introduced with Win 95. Binary database of information

Software HelpSoftware Help

Control Panel – Graphical “window” to the Registry

Device Manager – Another graphical path to the Registry

REGISTRY EDITOR(s): REGEDIT REGEDT32

Power On Self Test (POST)Power On Self Test (POST)

First thing to run when you start up computer

Waits for “power good” signal from power supply, then starts the CPU

FFFA is (almost) at the end of 1st meg of RAM, contains a “Jump Immediate” instruction to beginning of POST code

CPU instructs our “short list” items to check themselves out with own diagnostic

POST, cont.POST, cont.

Until video card is done, we are “in the dark” and could get “Beep Codes” for errors. Don’t memorize them. Constant beeping is either memory or video error.

Once the video card has checked itself out, we could get error codes/messages on the monitor as other devices report status

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POST, cont.POST, cont.

About this time, we get the option to run CMOS Setup routine

POST is done; control passes to “Bootstrap Loader.” It’s job is to find OS. Looks for the “Boot Sector” on floppy/hard disk

drive(s)A disk with functional OS is called a

“Bootable Disk” or “System Disk.” Could be floppy (DOS), CD or hard disk drive.

Boot OrderBoot Order

Somewhere in CMOS Setup is the ability to set the boot order, or the order in which the bootstrap loader will search for an OS.

I set my systems to: CD/DVD drive, floppy and then hard disk drive.

Usually, if a bootable CD is found, you get the option to boot from it (by pressing any key). Do nothing and loader continues the search for an OS.

POST CardsPOST Cards

Can be purchased; probably about extinct now.

I could have used one about three times in my career so far.

If another (known good) video card and/or memory won’t boot, motherboard is toasted.

Flashing the BIOSFlashing the BIOS

Mess up the process and motherboard is history

Won’t allow you to swap 486 for P4 chipMost processes require a bootable floppy

with special program and very odd command line

Some newer motherboards include Flash as Setup option.

I would rather eat a bug

UEFIUEFI

At least Sandy Bridge processor and current motherboard.

32/64-bit replacement for BIOSAllows use of 3 TB+ drives without

partitioning it downGood topic for an Internet search some rainy

Saturday

Thank YouThank You