Chapter 8 BIOS

Page 1

In this chapter, you will learn

how 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)

■ Maintain BIOS and CMOS

properly

The MCC isn’t just the memory

controller anymore, so let’s now call it the Northbridge

because it acts as the primary bridge between the CPU

and the rest of the computer. The Northbridge

deals with high-speed interfaces such as the connection

to your video card and RAM

The Southbridge works

mainly with lower-speed devices such as the USB controller

and hard drive controllers.

We call this set of Northbridge and Southbridge the

chipset

Modern processors include

the functions of the Northbridge

directly on the CPU. The

Southbridge is now called the

Input/Output Controller Hub

(ICH) in new Intel systems and

the Fusion Controller Hub (FCH)

in new AMD systems.

The chipset extends the data bus to every device on the PC. The CPU

uses the data bus to move data to and from all of the devices of the PC. Data

constantly flows on the external data bus among the CPU, chipset, RAM,

and other devices on the PC.

Every time you press a key on your keyboard, a scanning chip in the

keyboard notices which key you pressed. Then the scanner sends a coded

pattern of ones and zeros—called the scan code—to the keyboard controller.

The CPU doesn’t magically or otherwise automatically know how to talk

with any device; it needs some sort of support programming loaded into

memory that teaches it about a particular device. This programming is called

basic input/output services (BIOS)

In fact, every device on the computer needs BIOS!

You need some

type of permanent program storage device that does not depend on

other peripherals to work. And you need that storage device to sit on the

motherboard

ROM

Motherboards store the keyboard controller support

programming, among other programs, on a

special type of device called a read-only memory

(ROM) chip. A ROM chip stores programs, called

services, exactly like RAM: that is, like an 8-bit-wide

spreadsheet. But ROM differs from RAM in two

important ways. First, ROM chips are nonvolatile,

meaning that the information stored on ROM isn’t

erased when the computer is turned off. Second,

traditional ROM chips are read-only, meaning that

once you store a program on one, you can’t change

it. Modern motherboards use a type of ROM called

flash ROM that differs from traditional ROM in that

you can update and change the contents through a

very specific process called “flashing the ROM,”

Programs stored on ROM

chips—flash or any other kind

of ROM chip—are known

collectively as firmware, as

opposed to programs stored

on erasable media, which are

collectively called software.

System BIOS Support

Every system BIOS has two types of hardware to support.

1) First, the system

BIOS supports all of the hardware that never changes, such as the keyboard.

(You can change your keyboard, but you can’t change the keyboard

controller built into the Southbridge.) Another example of hardware that

never changes is the PC speaker (the tiny one that beeps at you, not the ones

that play music). The system ROM chip stores the BIOS for these and other

devices that never change

2) Second, the system BIOS supports all of the hardware that might change

from time to time. This includes RAM (you can add RAM), hard drives (you

can replace your hard drive with a larger drive or add a second hard drive),

and floppy drives (you can add another floppy drive, although that’s not

common today). The system ROM chip stores the BIOS for these devices, but

the system needs another place to store information about the specific details

of a piece of hardware.

A separate memory chip, called the complementary metal-oxide semiconductor

(CMOS) chip, stores the information that describes specific device

parameters. CMOS does not store programs; it only stores data that is read

by BIOS to complete the programs needed to talk

to changeable hardware. CMOS also acts as a clock

to keep the current date and time. Today,

the CMOS is almost always built into the Southbridge.

Most CMOS chips store around 64 KB of

data, but the PC usually needs only a very small

amount—about 128 bytes—to store all of the necessary

information on the changeable hardware.

Don’t let the tiny size fool you. The information

stored in CMOS is absolutely necessary for the PC

to function!

Device Drivers

A device driver is a file stored on the PC’s hard drive that contains all of

the commands necessary to talk to whatever device it was written to support.

All operating systems employ a method of loading these device drivers

into RAM every time the system boots.

Power-On Self Test (POST)

BIOS isn’t the only program on your system ROM. When the computer is

turned on or reset, it initiates a special program, also stored on the system

ROM chip, called the power-on self test (POST). The POST program checks

out the system every time the computer boots. To perform this check, the

POST sends out a command that says to all of the devices, “Check yourselves

out!”

Most modern PCs have only two beep codes: one for bad or missing

video (one long beep followed by two or three short beeps),You’ll hear three other beep sequences on most PCs (although they’re

not officially beep codes). At the end of a successful POST, the PC produces

one or two short beeps, simply to inform you that all is well.

The Boot Process sends a

signal down a special wire called the power good wire

to awaken the CPU.

This address is the

first line of the POST program on the system ROM!

That’s how the system starts the POST

the POST passes control to the

last BIOS function: the bootstrap loader. The bootstrap loader is little more

than a few dozen lines of BIOS code tacked to the end of the POST program.

Its job is to find the operating system. The bootstrap loader reads CMOS

information to tell it where to look first for an operating system.

Any device with a functional

operating system is called a bootable disk or a system disk.

preboot execution

environment (PXE). A PXE enables you to boot a PC without any local

storage by retrieving an OS from a server over a network.

Your CMOS needs a continuous trickle charge to retain its data. Motherboards

use some type of battery, usually a coin battery

Flash ROM chips can be reprogrammed to update

their contents. With flash ROM, when you need

to update your system BIOS to add support for a

new technology, you can simply run a small command-line

program, combined with an update file,

and voilà, you have a new, updated BIOS!