The presentation gives an idea to what the BIOS is related to the Personal Computer. It also describes the main functions of the BIOS in the PC

1. B I O S
(Basic Input Output System)
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2. ABBRIVIATIONS
• BIOS :- Basic Input Output System
• ROM :- Read Only Memory
• RTC :- Real Time Clock
• EEPROM :- Electrically Erasable Programmable
Read Only Memory
• OS :- Operating System
• CMOS :- Complementary metal–oxide–
semiconductor
• ESCD :- Extended System Configuration Data
• FDD :- Floppy Disc Drive
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3. B I O S Intro….
• BIOS or Basic Input Output System is provided on
Read Only Memory (ROM) ICs as an interface
between the PC Hardware and Operating System.
• In early PCs the BIOS was stored on a ROM or an
EEPROM
• In the past several years a specific type of
EEPROM called "Flash" is typically used to
contain the BIOS program.
• These can be reprogrammed without being
removed from the PC. This is called a Flash Bios.
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4. B I O S ..detailing
• PC systems have other BIOS software known as
“Adapter BIOS” contained in peripheral devices.
• The BIOS ROMs in a PC system are : System
(Main or Mother Board) BIOS , Video BIOS, Drive
Controller BIOS, Network Board BIOS and SCSI
BIOS.
• American Megatrends Incorporated (AMI), Award
and Mr. BIOS are some of the providers of BIOS.
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5. OS & BIOS
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OS can access standard functions
contained in the BIOS.
Operating
System
& A P Is
B I O S
PC Hardware :
Disk controller, Buses,
Video, CPU, Memory,
embedded Circuitry

6. FUNCTIONS of BIOS
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Functions ( Parts ) of BIOS :
POST
Routines
CMOS
Setup
System
Service
Routines
In general there are three functions or three parts of BIOS
1.P O S T routines
2.C M O S setup and
3.System service routines

7. P O S T ROUTINES
First Part
• Power On Self Test (P O S T)routines handles
the system startup.
• Checking the system components &
initialization process.
• P O S T reads the CMOS section for Hardware
settings.
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8. CMOS SETUP
CMOS RAM setup (Second Part)is required for maintaining
Hardware configuration.
• It is typically combined on the same IC with the Real Time
Clock- RTC.
• Generally the PC Motherboards have 256 Bytes low power
static battery backup CMOS RAM.
• Battery backup maintains the system date, time and
parameter setting intact and ESCD ( Extended System
Configuration Data ) information needed by the PC’s Plug-
and- Play.
• The CMOS configuration setup includes scores of advanced
settings and some essential ones such as Hard Disk, FDD, Date
& Time, Boot Sequence etc.
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9. SYSTEM SERVICE ROUTINES
Third part or third function of B I O S
•The system services include routines for Keyboard,
Printer, Disk Drives, parallel & serial ports, Video
etc.
•These are sets of individual functions ( programs)
that form the layer between hardware and
operating system.
•It is this interface which enables the O S to work
on any Mother Board design, bus architectures,
processor types & chipsets.
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10. SYSTEM SERVICE ROUTINES
• As the technology dealing with these PC devices
advances, BIOS must also advance to provide the
required interface to the OS.
• Services are called by using Microprocessor
interrupts.
• Latest updated BIOS versions provide service
routines essential for state of art advancements
in devices & standards such as Disk
Interfaces( ATA-100), Video ( AGP), USB2, Power
Management features etc.
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11. P O S T in a PC System
• Once the system is powered, it checks hardware.
 Test the CPU
 Initialize Support chips & chipsets.
 Initialize Keyboard & controller.
 Test ROM BIOS & CMOS ( Checksum )
 Memory Test
 Initialize external cache
 Initialize vector table
 Video Test
 DMA, PCI & other buses test
 Mouse initialization
 Floppy Test, Hard Drive Test
 Serial, Parallel port test
 Initialize Other adaptor ROMs ( BIOSes )
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