bios
DESCRIPTION
The slides describe how the Basic Input Output System (BIOS) functions on a PCTRANSCRIPT
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BIOSEvans Lampi
University of Zambia
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BIOS BIOS stands for basic input/output
system BIOS consists of low-level software that
controls the system hardware. BIOS acts as an interface between the
operating system (OS) and the hardware.
BIOS consists of device drivers, or just drivers
BIOS is a link between hardware and software in a system.
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BIOS BIOS consists of software that interfaces
the hardware to the OS
is preloaded into read-only memory (or ROM), and some is loaded into RAM from disk.
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BIOS AS INTERFACE TO HARDWARE
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BIOS AND PC STARTUP Motherboard ROM
Adapter card ROMs (such as that found on a video card)
Loaded into RAM from disk (device drivers)
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BIOS ROM Non volatile
Software used to be burned into ROM
Drivers were self-contained, preloaded into memory, and accessible any time the PC was powered on.
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ROM AND POST ROM chip also contained a power-on self
test (POST) program and a bootstrap loader.
POST initiates the loading of an OS by checking for and loading theboot sector from a floppy or hard disk
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DRIVERS Low level routines
Originally all drivers were stored in the BIOS ROM on the motherboard.
OS called on the drivers to interact with the hardware
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LIMITATIONS OF ROM BIOS What happens when new hardware is
added?
ROM is read only and therefore cannot be changed.
New hardware has to come with adapter cards that have their own BIOS ROMs
ROM was programmed to scan a predetermined area of memory looking for any adapter card ROMs
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DRIVERS ON BOOT DRIVE Drivers placed on the boot drive
Drivers loaded into RAM during loading of OS
MS-DOS startup file (IO.SYS) checked for a configuration file (called CONFIG.SYS)
CONFIG.SYS specified any additional drivers to load to support new hardware.
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SOFTWARE INTERRUPT Application through the OS calls to a
specific software interrupt.
the interrupt vector table would then route the call to the specific part of the BIOS (meaning the specific driver) for the device being called.
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FIRMWARE portion of the BIOS contained in ROM
chips
Found on the motherboard and in some adapter cards
drivers in nonvolatile ROM remain intact after power is turned off
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MODERN IMPLEMENTATION Motherboard BIOS only loads the basic
routines to start up the PC
Drivers are stored on the hard drive
Drivers are loaded into RAM are run from RAM (which is faster)
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PC LAYERS
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LAYERS SYSTEM purpose of the layered design is to
enable a given OS and applications to run on different hardware
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API application programming interface (API)
Consists of the various commands and functions the OS can perform for an applicatione.g.an application can call on the OS to load
or save a file Application does not need to know the
specifics on how to drive particular hardware.
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BIOS AND CMOS RAM BIOS is sometimes confused with CMOS
CMOS is a RTC/NVRAM CMOS stores the configuration file
BIOS setup
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MOTHERBOARD ROM BIOSPerforms POST Setup Bootstrap loader BIOS
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POST tests computer’s
ProcessorMemoryChipsetvideo adapterdisk controllersdisk drivesKeyboardand other crucial components
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SETUP configuration and setup program activated during POST by pressing a key
(e.g. F1) enables configuration of
motherboard and chipset settings date and timePasswordsdisk drivesand other basic system settings
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BOOTSTRAP LOADER A routine that reads the first physical
sector of various disk drives looking for a valid master boot record (MBR)
MBR ends with signature bytes 55AA the code is then executed MBR program code then reads the first
physical sector called the volume boot record (VBR)
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VBR loads the first OS startup file, which is
IO.SYS (Windows 9x/Me), ntldr (Windows XP/2000/NT), bootmgr (Windows 7/Vista).
The OS is then in control and continues the boot process.
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BIOS refers to the collection of actual drivers
that act as a basic interface between the OS and hardware
When running DOS or Windows in Safe mode, you are running almost solely on ROM-based BIOS drivers
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ROM CHIP TYPESThe four main types of ROM chips that have been used in PCs are as follows: ROM—Read-only memory PROM—Programmable ROM EPROM—Erasable PROM EEPROM—Electrically erasable PROM,
also sometimes called a flash ROM
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PROM PROGRAMMER
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EPROM CHIP
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EPROM ERASER
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ROM TYPES ROM onboard, including the following: Video cards—All have an onboard
BIOS. RAID (Redundant Array of
Independent Disks) cards Network card. ATA/Serial ATA (SATA) or floppy
upgrade boards Y2K boards
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CHAPTER 5 SECTIONS COVERED BIOS Basics Motherboard ROM BIOS ROM Hardware