Computer Hardware

Ministry of Higher EducationBamyan University

Computer Science Department

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Presented by : Mustafa Kamel Mohammadi

Email : bamian.cs@gmail.com

BIOS and BOOT process

learning objective

In this chapter you will learn and answer to the following questions What is BIOS?

BIOS manufacturers

Booting computers and steps in this process

What is CMOS?

BIOS manufacturers

BIOS upgrading process

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Introduction

• When you push Power button there is nothing in memory to be done, so something must be done from scratch

• System BIOS (Basic input output system) do all things need to start a system

• Contains the first instruction that turns the computer on.

• The three basic functions of BIOS are:• Boots the computer• Validates PC configuration• Interface between PC hardware and their software

• Interface that connects CPU with all I/O devices

• All CPU interaction with I/O devices are through BIOS

• In addition to the system BIOS, there are BIOSs to control the peripheral devices that have been added to the computer

• For example, most video cards, hard disks, and SCSI adapters have a BIOS that controls parts of their interaction with the processor and other motherboard components.

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BIOS manufacturer

• AMI ( American megatrends Inc)• Once one of the providers of BIOS chips for intel motherboard producer

• Phoenix• Over 80% of intel boards now uses Phoenix BIOS ROM

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Booting the computer

• The process of starting a computer up is called boot process

• The boot process is done under the guidance of BIOS

• BIOS is in charge of all actions taking place behind the scene

• Boot process is a complex process

• Varies between manufacturers but contains these steps• Verifies configuration

• Checks the hardware

• Load the software

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System boot sequence

• 1: power supply initialize itself• It does not provide power to all motherboard components immediately, but Transmits a power signal

to motherboard chipset ,that sends a system reset command to CPU

• 2: CPU is activated• System reset command cause CPU to read first instruction from JUMP address• JUMP address is a fixed location in system memory• JUMP address the physical address of BIOS program on BIOS ROM

• 3: CPU starts execution• Starts running BIOS program copied from BIOS ROM

• 4: POST (Power on Self Test) is done• Verifies and test all the hardware configuration• If any error is detected it sounds with beep codes with system sound, because no other I/O is loaded a

this time.

• 5: After POST is done without errors• System BIOS Starts video adaptor by Video Adaptors BIOS• Each device has it’s own BIOS besides system BIOS

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Cont.

• 6: Video Display is activated• Contains information about the BIOS program

• 7: other Device’s BIOS routines are started

• 8: BIOS perform a series of tests

• 9: system BIOS checks devices listed in CMOS are present and functioning

• 10: if BIOS supports PnP , each device is configured

• 11: displays a summery data screen

• 12: start operating system by finding operating system in CMOS configuration• If Hard disk is the boot drive, it selects from master boot record (MBR)

• If no boot device is found, displays an error indicating no boot device available

• And finally the PC is up and running

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Cold boot vs. Warm boot

• 1: Cold boot

• The boot sequence used when a PC is powered on from a powered off condition is called a cold boot.

• A cold boot is done when the computer is started from a cold (or completely powered off) status.

• A cold boot causes the complete boot and POST sequence to run.

• 2: Warm boot

• A warm boot happens when the PC is already powered on. Pressing the key combination CTRL-ALT-DEL or pressing the reset button causes the system to wake up.

• The POST process does not run after a warm boot

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BIOS beep codes

• Not all beep codes mean something dangerous has happened

• All BIOS program sound a single beep when all is done well

• If something bad had happened single beep means different

• You should figure out what those beep codes mean

• Different BIOS chips vendors has different standards for beep sound codes

• Beep codes contains short beeps, long beeps and varying number of beeps

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Bios start up screen

• If POST is done successfully, BIOS loads the video adaptor and computer has display

• BIOS then display its start up screen that contains the following info:• Name and logo of BIOS manufacturers

• Serial and version number of BIOS

• The keyboard key that allows to access the BIOS set up program

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CMOS (Complementary Metal-Oxide Semiconductor)

• The configuration data for a PC is stored by the BIOS in what is called CMOS.

• Those configurations include:• System configuration, including any modifications made to the system, its hard drives, peripheral

settings, or other settings. • The system and RTC (real-time clock) settings are also stored in the CMOS

• CMOS is also known as NVRAM (nonvolatile RAM)

• Requires very little power (about one-millionth of an amp) to retain any data stored on it

• CMOS usually refers to the storage of the computer’s hardware configuration data.

• When the computer is started up, the CMOS data is read and used as a checklist to verify that the devices indicated are in fact present and operating.

• Once the hardware check is completed, the BIOS loads the operating system and passes control of the computer to it.

• From that point on, the BIOS is available to accept requests from device drivers and application programs for hardware assistance

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BIOS configurations

• Security and setting following passwords• User password : controls the boot process

• Supervisor password : controls access to BIOS configuration

• Power management options

• IDE devices setup

• Integrated I/O devices controller configuration

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BIOS updates and Flash BIOS

• Old system required to change the entire BIOS chip for upgrading BIOS

• Drawbacks of changing ROM was• Motherboard damage• ESD (Electro static discharge)• Bent pins

• After EEPROM replaced PROM and EPROM this process got easier using Flashing.

• Flashing is the process used to upgrade your BIOS under the control of specialized flashing software.

• Any BIOS provider that supports a flash BIOS version has flashing software and update files available either by disk or as a downloadable module from its Web site.

• Four thing are needed to upgrade a BIOS• A flash BIOS• Serial number and version• Flashing software• Upgrade Files

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References

• “PC hardware a beginner’s guide” by Ron gilster

• “PC architecture by Michael Karbo” 2005

• “Illustrated guide to PC hardware” by Michael karbo 1998

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