1. Chapter 4:
Motherboard and BIOS

2. Buses
Both the External Data Bus and the Address Bus connect all the parts on the motherboard
There are two of each of these buses, one of each between the CPU and the chipset, and the other two are between the chipset and everything else (except RAM)

3. BIOS BIOS: Basic Input/Output Services
A BIOS is a collection of programs that tell the CPU how to communicate with the most basic parts of your computer
Each program is called a service
These programs are tiny, usually 2 to 30 lines of code each

4. ROM A BIOS is stored on a ROM ROM = Read Only Memory
ROM chips are nonvolatile, meaning that they do not lose their data when they lose power
They are also read-only, which means that the programs on them can’t be changed

5. Hardware Groups Core Group - common, necessary, unchangeable devices
Examples are keyboard, chipset, support chips
CMOS group – common, necessary devices that may be changed
Examples are Hard Drive, Floppy Drive, RAM
Everything Else group – non-core devices such as mice, sound cards, and CD-ROM drives

6. System BIOS
The system BIOS is the collection of BIOS programs that interface with the Core group of hardware in a PC
The system BIOS comes with the motherboard, and is stored on the system ROM

7. System ROM Stores system BIOS
Usually comes in a DIPP packaging, and most have a shiny label
The majority of system ROMs store 64k of data
Like all ROM chips, the system ROM is nonvolatile
Almost never fails, although when it does, it can be catastrophic

8. CMOS CMOS – Complementary Metal Oxide Semiconductor
CMOS chip also acts as a real-time clock for the computer
CMOS chips do not store programs, they store only the data read by BIOS to access changeable devices
Usually store 64k, but about 128 bytes are usually used

9. CMOS Setup
In order to change CMOS data, you need to use a program built into the system ROM called the CMOS setup program
It is started while the PC boots up, after it is turned on and before it loads an OS
Accessed in many different ways, look through your motherboard manual to find out how to access yours

10. CMOS Setup
All CMOS Setup menus will appear differently, but they do most of the same things
On the Standard CMOS Setup screen, the time/date, hard drive, and floppy drive settings can be changed
Other than that, all BIOS have different settings that can be changed, which are explained in your motherboard’s manual

11. More CMOS
Because CMOS is changeable, it requires power to keep its settings
Power is usually supplied by a battery, which is either 3.3 or 6 volts
The battery is also usually Ni-Cad or Lithium Ion cells, and last about 5-7 years
When the battery dies, you either must buy a new motherboard, or hope that your motherboard has a connector for an external battery, which most modern ones do not

12. Flash ROM ROM has a huge shortcoming:
Because it is read-only, you have to replace the ROM chip to update the BIOS
Because of this, Intel developed something called a Flash ROM
Flash ROM can be erased and updated using special command-line programs to accommodate things such as new processors
Also nonvolatile

13. Flash ROM
Because the Flash ROM is reprogrammable, data that is usually stored on a CMOS chip can now be stored on the System ROM
Although CMOS is virtually nonexistent now, the name “CMOS Setup” has stuck

14. Everything Else Group
Because IBM couldn’t predict every device that might be added to a PC, they gave a few ways to bring your own BIOS (BYOB)
These ways are:
Option ROM
Device Drivers

15. Option ROM
The first method of BYOB is to put the BIOS on the device itself
A card with an option ROM has a chip on it looking very much like the system ROM
This is because it is a ROM, and has the device’s BIOS stored inside it
Most BIOS on option ROM display information when you boot the system
In the early days of the PC, all devices had option ROMs, but today, option ROMs have been replaced by things such as device drivers, with one major exception: all video cards have their own BIOS for internal function

16. Device Drivers
A device driver is a file stored on a PC’s hard drive that contains all the BIOS commands to talk to a certain device
All operating systems load device drivers into RAM while they boot up, loading only the ones that are needed via the use of a “list” of device drivers
This list can be in a variety of formats: a text file, many text files, or, in the case of Windows 95/98/2000, a special database

17. Device Drivers
Without these files, the OS doesn’t know which device drivers to load
As far as the PC is concerned, if a device driver isn’t loaded for a device, that device doesn’t exist

18. Device Drivers
Some of the configuration files and their corresponding OS are:
config.sys – MS-DOS, still loaded in Windows 9x for DOS compatibility
system.ini – Windows 9x/2000, not required by Windows 2000
Windows Registry – Windows 9x/2000

19. Windows Registry
The Windows Registry is an extremely complex binary file
It stores all the configuration data in Windows 9x/2000
The Registry is rarely accessed directly
The Control Panel and the Device Manager provide a much more user-friendly way to access the Registry
If the registry is accessed directly, it is done using the Registry Editor

20. Control Panel
The Control Panel contains applets that allow the user to change a broad range of system settings
Each version of Windows has many applets in common with the others, but it also has its own unique applets
Some third-party software programs add their own applets, such as Apple Quicktime or Real Networks RealPlayer

21. Device Manager
Using the Device Manager, the user can change or remove the driver for any device installed in the computer
The device manager is not used to install new hardware, that is done with the Add/Remove Hardware applet

22. Registry Editor
In Windows 9x, the Registry editor is a program called REGEDIT.EXE
In Windows 2000, it is a program called REGEDT32.EXE
REGEDT32 is much more powerful than the Windows 9x REGEDIT
Setting a value wrong in the Registry can potentially kill any Windows system, so you must be careful when accessing it directly

23. POST POST – Power On Self Test
Every time a PC boots, it initiates a special program also stored on the system ROM called the Power On Self Test
The POST sends a message to every device telling each to check itself out
If a core device is not working, the POST will issue a series of short beeps through the system speaker that correspond to certain errors
If a non-core device is not working, a corresponding error will be displayed on the screen

24. Boot Process
The first step in the boot process is to initialize the CPU itself by charging a special wire called power good
As soon as the CPU is “woken up”, it automatically starts the POST
After POST is finished, the computer has to be able to find the programs on the hard drive to load an OS
This is done with a BIOS function called the bootstrap loader

25. Bootstrap Loader
The bootstrap loader is little more than a few dozen lines of BIOS code tacked on the end of the POST program that looks for an OS
First it searches the floppy drives to see if a disk is inserted, and if a disk is inserted, assumes there is an OS on the floppy
If a disk is not inserted, it proceeds to search the hard drive
If a disk is bootable, it will contain special code telling the computer where to locate the OS
A disk with a functioning OS is called a system disk or bootable disk

26. Motherboards Motherboards come in a large variety of sizes
The most popular layout today is called ATX, followed distantly by the old AT formfactor

27. AT Motherboards Two different sizes of AT motherboards exist
Regular AT, or AT – the original size, about the size of two 8.5x11 sheets of paper placed next to each other
Baby AT – much smaller size of the AT motherboard
The only dedicated connector on an AT motherboard is the keyboard connector, so expansion cards must be used to add anything else, including serial and parallel ports along with PS/2 style mouse ports, leaving little room for other expansion cards
Because of this, a new formfactor was needed

28. ATX Motherboards ATX was designed to replace AT
It had PS/2 keyboard and mouse connectors, serial ports, a parallel port, and after their invention, USB ports onboard, eliminating the use of expansion cards to use these ports
Also uses a different power connector than AT boards
Enables better air movement with position of the power supply
Uses “soft power”, a feature that enables the computer to be turned on and off using software

29. ATX Motherboards ATX motherboards have three sizes:
Standard ATX – the original ATX formfactor
Micro ATX – about 30% smaller than ATX, but uses standard ATX connections
Flex ATX – even smaller than Micro ATX, usually use a special Flex ATX power supply