BIOS
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Objectives
• In this chapter, you will:
-Learn to define the BIOS and understand how it
relates to CMOS
-Learn how to determine which BIOS is running on a
PC
-Identify and explain the key types of BIOS
-Perform a BIOS upgrade
-Open and manipulate the BIOS Setup
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BIOS Basics
• BIOS is a term that stands for basic input/output system. BIOS is
really the link between hardware and software in a system. Most
people know the term BIOS by another name device drivers, or just
drivers.
• What can be confusing is that some of the BIOS is burned or
flashed into a ROM chip that is both nonvolatile (it doesn't get
erased when the power is turned off) and read-only.
• The BIOS also includes ROM chips installed on adapter cards, as
well as all the additional drivers loaded when your system boots
up.
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BIOS
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In IBM PC Compatible computers, the Basic Input/Output System (BIOS) , also
known as the System BIOS.
The BIOS is boot firmware, designed to be the first code run by a PC when
powered on.
The initial function of the BIOS is to identify, test, and initialize system devices
such as the video display card, hard disk, and floppy disk and other hardware.
This is to prepare the machine into a known state, so that software stored on
compatible media can be loaded, executed, and given control of the PC. This
process is known as booting, or booting up, which is short for bootstrapping.
BIOS programs are stored on a chip and are built to work with various devices
that make up the complementary chipset of the system. They provide a small
library of basic input/output functions that can be called to operate and control
the peripherals such as the keyboard, text display functions and so forth.
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BIOS Basics
• The combination of the motherboard BIOS, the adapter card BIOS,
and the device drivers loaded from disk contribute to the BIOS as a
whole.
• The portion of the BIOS contained in ROM chips both on the
motherboard and in some adapter cards is sometimes called
firmware, which is a name given to software stored in chips rather
than on disk.
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BIOS Basics
• In principle, the BIOS in ROM was customized to the
particular manufacturer's hardware, allowing low-level
services (such as reading a keystroke or writing a sector of
data to diskette) to be provided in a standardized way to
the operating system.
• For example, an IBM PC might have had either a
monochrome or a color display adapter, using different
display memory addresses and hardware - but the BIOS
service to print a character on the screen in text mode
would be the same.
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BIOS Hardware/Software
• The BIOS in a PC comes from three possible sources:
-Motherboard ROM
-Adapter card ROM (such as that found on a video card)
-Loaded into RAM from disk (device drivers)
• The motherboard ROM BIOS is most often associated with hardware
rather than software. This is because the BIOS on the motherboard is
contained in a ROM chip on the board, which contains the initial
software drivers needed to get the system running.
• The motherboard BIOS usually includes drivers for all the basic system
components, including the keyboard, floppy drive, hard drive, serial
and parallel ports, and more.
• As systems became more complex, new hardware was added for which
no motherboard BIOS drivers existed. These included devices such as
newer video adapters, CD-ROM drives, SCSI hard disks, USB ports,
and so on.
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BIOS Hardware/Software
• Rather than requiring a new motherboard BIOS that would specifically
support the new devices, it was far simpler and more practical to copy
any new drivers that were necessary onto the system hard disk and
configure the operating system to load them at boot time.
• Some drivers must be active during boot time. For example, how could
you boot from a hard disk if the drivers necessary to make the disk
interface work must be loaded from that disk?
• Computer manufactures designed the motherboard ROM to scan the
slots looking for adapter cards with ROMs on them.
• If a card was found with a ROM on it, the ROM was executed during
the initial system startup phase, before the system began loading the
operating system from the hard disk.
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BIOS Hardware/Software
• By putting the ROM-based drivers right on the card, you didn't have to
change your motherboard ROM to have built-in support for new
devices. A few cards (adapter boards) almost always have a ROM
onboard, including the following:
-Video cards. All have an onboard BIOS.
-SCSI adapters. Those that support booting from SCSI hard drives or CDROMs have an onboard BIOS.
-Network cards. Those that support booting directly from a file server have
what is usually called a boot ROM or IPL (initial program load) ROM onboard.
This enables PCs to be configured on a LAN as diskless workstations-also
called Net PCs, NCs (network computers), or even smart terminals.
-IDE or floppy upgrade boards. Boards that enable you to attach more or
different types of drives than what is normally supported by the motherboard
alone.
-Y2K boards. Boards that incorporate BIOS fixes to update the century byte in
the CMOS RAM.
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BIOS and CMOS RAM
• Some people confuse BIOS with the CMOS RAM in a system. This
confusion is aided by the fact that the Setup program in the BIOS is
used to set and store the configuration settings in the CMOS RAM.
They are, in fact, two totally separate components.
• The BIOS on the motherboard is stored in a fixed ROM chip. Also on
the motherboard is a chip called the RTC/NVRAM chip, which stands
for real-time clock/nonvolatile memory.
• Although it is called nonvolatile, it is actually volatile, meaning that
without power, the time/date settings and the data in the RAM portion
will, in fact, be erased.
• It is called nonvolatile because it is designed using complementary
metal-oxide semiconductor (CMOS) technology, which results in a chip
that runs on very little power.
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BIOS and CMOS RAM
• A battery in the system, rather than the AC wall current, provides that
power.
• This is also why most people incorrectly call this chip the CMOS RAM
chip; although not technically accurate, that is easier to say than the
RTC/NVRAM chip.
• When you enter your BIOS Setup, configure your hard disk parameters
or other BIOS Setup settings and save them, these settings are written
to the storage area in the RTC/NVRAM (otherwise called CMOS
RAM) chip. Every time your system boots up, it reads the parameters
stored in the CMOS RAM chip to determine how the system should be
configured.
• A relationship exists between the BIOS and CMOS RAM, but they are
two distinctly different parts of the system.
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Motherboard BIOS
The BIOS is a collection of programs embedded in one or more chips, depending on
the design of your computer. That collection of programs is the first thing loaded
when you start your computer, even before the operating system. Simply put, the
BIOS in most PCs has four main functions:
-POST (power on self test). The POST tests your computer's processor, memory,
chipset, video adapter, disk controllers, disk drives, keyboard, and other crucial
components.
-Setup. System configuration and setup program. This is usually a menu-driven
program activated by pressing a special key during the POST, which enables you to
configure the motherboard and chipset settings along with the date and time,
passwords, disk drives, and other basic system settings.
-Bootstrap loader. A routine that reads the disk drives looking for a valid master
boot sector. This master boot sector program then continues the boot process by
loading an operating system boot sector, which then loads the operating system core
files.
-BIOS (basic input/output system). This refers to the collection of actual drivers
used to act as a basic interface between the operating system and your hardware
when the system is booted and running.
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Shadow ROM
• ROM holds the BIOS, POST, and the program to boot the drives.
• ROM has a much longer access time than RAM, slowing down the
system.
• If, on boot up, the ROM is copied into RAM, the system now can
access this fast RAM that is shadowing the slow ROM,
considerable speeding up the overall system operation
System BIOS shadowed
Video BIOS shadowed
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ROM
(Read-Only Memory)
Characteristics:
– ROM chips contain vital, permanently stored information written
to them by the manufacturer.
– ROM is nonvolatile in that the information remains stored
regardless of whether an electrical current is present.
– ROM is non-changeable in that it can’t be written over, only read
from.
– This is why it’s called read-only chip. Information on a ROM chip
never changes. If an error occurs on the chip, it must be
replaced.
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Programmable ROM
Formal name for a ROM chip that can’t be modified is mask ROM (from the
chip’s manufacturing mask).
PROM Chip
Hybrid ROM chips:
• PROM: Programmable ROM chips require a special type of machine
called a “PROM programmer” or “Prom burner” and can be changed
one time. The chip is shipped blank, and the programmer “burns in”
specific instructions. From that point, chip can’t be changed.
• EPROM: Erasable Programmable ROM chips use the PROM burner, but
can be erased by shining ultraviolet (UV) light through a window in the
top of the chip.
EPROM Chip
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EEPROM Chip
• EEPROM: Electrically erasable programmable ROM chips can be
erased by an electrical charge and written to using slightly higherthan-normal voltage. Can be erased one byte at a time, rather than
the entire chip.
• Flash ROM: Also called flash RAM or flash memory. Stores data much
like EEPROM but use a super-voltage charge to erase a block data
(rather than a byte).
• Most systems today use Flash memory. Flash is truly nonvolatile
memory that is rewriteable, enabling users to easily update the ROM
or firmware in their motherboards or any other components such as
video cards, SCSI cards, peripherals, and so on.
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CMOS RAM (RTC/NVRAM )
A special chip combining a Real-Time Clock (RTC) and at least 64
bytes of Non-Volatile RAM (NVRAM)
In Pentium class
computers, it
consumes a portion of
Stores configuration
the Super I/O Chip
settings
Original AT CMOS
•Referred to as CMOS
because it is on a
Complementary Metal
Oxide Semiconductor
•Eliminates the need for jumpers and
switches used for the configuration
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PnP (Plug ‘n’ Play)
• Workable auto configuration process involving more than only the
operating system.
• Auto configurations is where the computer tries to interpret any
new adapter card on the expansion bus and then to integrate the
peripheral.
• Once configured, PnP operating system will assign various system
resources.
• PnP involves intercommunication between the hardware devices
in the system and operating system that controls how they work
together.
• Three aspects of PnP:
– PnP compatible hardware.
– PnP BIOS.
– PnP operating system. (Win 95, Win NT5, OS/2)
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Virus attacks
• There was at least one virus which was able to erase Flash
ROM BIOS content, rendering computer systems unusable.
CIH, also known as "Chernobyl Virus", affected systems
BIOS and often they could not be fixed on their own since
they were no longer able to boot at all.
• To repair this, Flash ROM IC had to be ejected from the
motherboard to be reprogrammed somewhere else.
Damage from the CIH virus was possible since most
motherboards at the time of CIH propagation used the
same chip set, Intel TX, and most common operating
systems such as Windows 95 allowed direct hardware
access to all programs.
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ROM BIOS STARTS POST
ROM BIOS
1. Check all hardware
2. Run Boot Program
3. Read Boot Record
With instructions from ROM
BIOS CPU tests all Hardware
Components. After all
components pass POST the
system beeps once.
4. Load IO.SYS
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FIND BOOT RECORD
ROM BIOS
1. Check all hardware
ROM BIOS Instructs CPU
to look for the Boot Record
2. Run Boot Program
3. Read Boot Record
4. Load IO.SYS
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LOAD BOOT RECORD
ROM BIOS
1. Check all hardware
2. Run Boot Program
3. Read Boot Record
4. Load IO.SYS
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LOAD IO.SYS
ROM BIOS
1. Check all hardware
2. Run Boot Program
3. Read Boot Record
4. Load IO.SYS
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