BIOS

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BIOS

• BIOS Basic Input Output System
• BIOS all the drivers in a system working
  together to act as an interface between the
  hardware and the operating system software
• BIOS is also called Device Drivers

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BIOS

• PC BIOS comes from three possible sources
• Motherboard BIOS
• Adapter BIOS
• Device drivers loaded from disk
• BIOS contained in ROM chips is sometimes called
  firmware
• Purpose of BIOS To enable a given OS and
  applications to run on different HW

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BIOS
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BIOS

• OS never talks to hardware directly instead it
  must always go through appropriate device drivers
• Devices which dont need to be active during boot
  timeDevice drivers not in ROM but loaded from
  disk.
• Why? Which devices must be active during boot
  time?

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BIOS

• Devices which must be available during boot-time
• Floppy disk
• Hard disk drive
• Video card
• Keyboard

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Adapter BIOS

• Example Video
• Motherboard might be used with many video cards
• its not possible/economical to include video
  BIOS on the motherboard
• BIOS located on Adapter board
• Other Adapter BIOS
• SCSI adapter Network cards IDE cards

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Motherboard BIOS

• Held in ROM or Flash
• Components
• Power On Self Test (POST)
• Setup Program (activated by special key during
  POST)
• Bootstrap loaderScans disk drives for valid
  master boot sector
• BIOS routines

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Motherboard BIOS

• Motherboard BIOS address ranges
• 0E0000h-0FFFFFh (128kB BIOS)
• 0F0000h-0FFFFFh (64kB BIOS)
• Other addresses 0C0000h upwards are available for
  BIOS routines
• Intel processors power up in real mode
• Reset CS0FFFFh IP0h

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Adapter BIOS

• Adapter board ROMs are scanned by motherboard
  BIOS during POST
• Scanned range 0C0000h-0DFFFFh
• Signature 55AAh indicates start of a ROM

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PC Boot Process

• Initialisation of primary output device (display)
• Initialisation of primary input device (keyboard)
• POST
• Scan of system busses (e.g. PCI) for PnP option
  ROM headers
• BIOS performs resource conflict resolution and
  allocation
• BIOS displays a prompt that the operator uses to
  enter the Setup Utility
• BIOS reads settings from non-volatile memory
• Scan of system busses (e.g. PCI) for PnP
  expansion headers
• PnP initialisiation, ID assignments, IPL and
  BCV priority lists
• System BIOS saves settings to non-volatile memory
  and boots system

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Motherboard CMOS RAM

• Original PC ATMotorola 146818 RTC and CMOS RAM.
  10B 54BPC AT used the 54B for storing system
  configuration
• Modern PCsNon-volatile memory typically in
  Super I/O. Modern systems often require 2-4kB to
  store configuration (mainly for PnP support)

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XT Motherboard (8088)
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P6 Motherboard (440LX Chipset)