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

2. The 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

3. RAM
Northbridge
CPU
Address Bus
EDB

4. RAM
Northbridge
CPU
Address Bus
EDB
Southbridge
keyboard
Video Card
Hard Disk Drive

5. Chipset
Address Bus
Northbridge
RAM
CPU
EDB
Chipset
Southbridge
Keyboard
Controller
Video Card
Hard Disk Drive

6. 845 Chipset

7. 925 Chipset

9. Keyboard
How we communicate with the keyboard

10. Problems Different motherboards have different keyboard controllers
We need specific code to talk to the controller
We need a place to store this specific programming and the programming for other devices (optical drive, floppy, etc.)

11. Solution
Use a ROM chip
Does not “forget” when power is removed, like RAM does
Specific to motherboard and devices on it
Read only, code does not change
Can hold lots of programs, like a “chapter book”
Called “firmware”

12. IBM’s BIOS
BIO
BIOS
Patent “fence” around BIOS

15. Making a ROM chip
We “burn” the code into the chip: 1

16. System ROM Holds all the support programming for basic devices
Is given a specific address space, or range of memory addresses for its code

17. The First Megabyte Upper Memory Conventional Memory 1 MB (384 KB)
Address 0

18. Basic Hardware CPU Mouse Keyboard Video card RAM Network card
Sound Card
Floppy drive
Hard Disk drive
Zip drive
USB ports
CD-ROM drive

19. Basic Hardware CPU Mouse Keyboard Video card RAM Network card
Sound Card
Floppy drive
Hard Disk drive
Zip drive
USB ports
CD-ROM drive

20. Stored Information Stores access/write code for keyboard
Stores access/write code for system speaker
Stores access/write code for other chips (functions) on motherboard
Does not change (more on this in a moment)

21. CMOS 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

22. Chipset
Address Bus
Northbridge
RAM
CPU
EDB
Chipset
Southbridge
BIOS
And
CMOS
Keyboard
Controller
Video Card
Mouse 20

23. BIOS
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.

24. BIOS information
CMOS information

25. CMOS 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 Setups
You should only get to Setup on purpose
Program stored in BIOS, but only edits data in CMOS
First CMOS was set of switches!

28. Who makes BIOS? Award Software Phoenix Technologies
AMI – American Megatrends Inc.
They write BIOS with lots of options; motherboard maker picks sections to be used
Long gone are IBM’s patents on BIOS
Same parent company

29. Setup Lots of screens and subscreens
You don’t need to know about all settings on all screens
Motherboard book is mildly helpful on some options
You should know generally where things can be found

30. 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)

34. Here is where you set the boot order

35. When adding a modem, you might want to turn both of these off.

38. Old 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

39. New 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.

40. Chip Evolution
EPROM – Erasable Programmable ROM; used ultra-violet light (sunlight) to erase
EEPROM – Electrically Erasable – what we use today
Flash ROM – another name for EEPROM
NVRAM – Non-volatile RAM. Really not so, still needs battery power

41. The 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

42. Easy way to spot this chip is by the shinny label

43. About that Battery Should last 5 to 10 years
You can find them at Savon even
If your system forgets date and/or time, it’s time to replace the battery
Beware the evil ESD!

44. More Battery Sometimes 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 battery
Do either for about 10 seconds
If you are to pull battery, make sure you unplug system too

45. 10

46. More 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

49. Software 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

50. Software Help Control Panel – Graphical “window” to the Registry
Device Manager – Another graphical path to the Registry
REGISTRY EDITOR(s):
REGEDIT
REGEDT32

53. 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

54. 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

55. 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.

56. Boot 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.

57. POST 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.

59. Flashing the BIOS Mess up the process and motherboard is history
Won’t allow you to swap 486 for P4 chip
Most 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

60. UEFI At least Sandy Bridge processor and current motherboard.
32/64-bit replacement for BIOS
Allows use of 3 TB+ drives without partitioning it down
Good topic for an Internet search some rainy Saturday

61. Thank You