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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
20
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
15
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
10
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
5
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