The document discusses BIOS (Basic Input/Output System), which is a program that allows communication between hardware and software components of a computer system. It summarizes key points about BIOS, including that BIOS initializes hardware components during startup, manages data flow between devices and the operating system, and is stored in a chip on the motherboard. The document also describes ROM, PnP, virus attacks targeting BIOS, and the startup process where the ROM BIOS performs POST and loads the boot record and IO.SYS files.

1. Name : Vanpariya itisha
Class: DC 3
Enrollment No: 92200938173
Subject:CHS
BIOS(Basic Input Output System)

3. BIOS Basic
• 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.
• The BIOS also includes ROM chips
installed on adapter cards, as well as
all the additional drivers loaded
when your system boots up.

4. Hardware VS Software

5. BIOS Hardware
• What Is BIOS Hardware?
• BIOS is the program a computer's
microprocessor uses to start the computer
system after it is powered on.
• It also manages data flow between the
computer's operating system (OS) and attached
devices, such as the hard disk, video adapter,
keyboard, mouse and printer.

6. BIOS Software
• What is BIOS software?
• BIOS software is one of the most important elements
that control the operation of your computer.
• BIOS is the system that prompts your computer's
operating system to start up when you turn on your
computer.
• BIOS is generally embedded in a chip on your
computer's motherboard.

7. Motherboard BIOS
The BIOS is a collection of programs embedded in one or more chips,
depending on the design of your computer. There Are the four main
functions of BIOS:
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
Bootstrap loader:-A routine that reads the disk drives looking for a valid
master boot sector.
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.
Motherboard

8. 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.
• 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.

9. 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

10. 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 is a
ROM chip never changes. If an error occurs on the chip,
it must be replaced.

11. 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 Chip:-
• PROM Chip:-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. PROM Chip EPROM Chip
EPROM Chip

12. 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.

13. Virus Attack
• 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.

14. ROM BIOS STARTS POST
ROM BIOS
1.Check All Hardware
2.Run Boot Program
3.Read Boot Record
4.Load IO.SYS
With instructions from ROM
BIOS CPU tests all Hardware
Components pass POST the
system beeps once.

15. Find BOOT RECORD
ROM BIOS
1.Check All Hardware
2.Run Boot Program
3.Read Boot Record
4.Load IO.SYS
ROM BIOS Instructs CPU to
look for the Boot Record

16. LOAD BOOT RECORD
ROM BIOS
1.Check All Hardware
2.Run Boot Program
3.Read Boot Record
4.Load IO.SYS

17. LOAD IO.SYS
ROM BIOS
1.Check All Hardware
2.Run Boot Program
3.Read Boot Record
4.Load IO.SYS