lec post , bios , cmos

Prepared BySamira Dayan Jayasekara

1. Startup BIOS runs power-on self test (POST) and assigns resources

2. ROM BIOS startup program searches for and loads an OS

3. OS configures the system and completes its own loading

4. Application software is loaded and executed

BIOS executes MBR program

◦ Turns to partition table to find OS boot record

Program in OS boot record attempts to find a boot loader program for OS

◦ Ntldr (Windows NT/2000/XP)

◦ Io.sys (Windows 9x)

Bridges connect the devices◦ But without a program, they don’t know how to

communicate

A special kind of program is required to enable the CPU to talk to other devices(that teaches the CPU about a particular device)

Perfect place to store the support programming is on the motherboard◦ On a special type of device called a read-only memory

(ROM) chip◦ Modern(A Flash ROM chip stores these programs)

These programs are collectively known as the basic input/output service (BIOS)

ROM chip stores programs exactly like RAM

Differs from RAM in two important ways◦ ROM chips are non-volatile Meaning that the information stored on ROM isn’t erased

when the computer is turned off

◦ Second, traditional ROM chips are read-only, Meaning that once a program is stored on one, it can’t be

changed

Modern motherboards use a type of ROM called◦ Flash ROM that differs from traditional ROM in that you

can update and change the contents through a very specific process called ―flashing the ROM

Each program is called a service

Programs stored on Flash ROM chips are known as firmware ◦ as opposed to program stored on erasable media that are

collectively called software

Keyboard controller

chip

Flash ROM chips can be reprogrammed

Download program from manufacturer

Copy program to floppy◦ Some programs will run within Windows

Boot to floppy and run program

Separate chip from ROM BIOS◦ Separate memory chip, called the complementary

metal-oxide semiconductor (CMOS) chip

Volatile (kept alive by battery)

Stores only changeable data ◦ Not programs◦ Acts as clock to keep data current◦ information that describes specific device

parameters

Customizable via SETUP program

Often on Southbridge

BIOS◦ Programs

◦ Non-volatile (stays same after power off)

◦ Can be changed by ―flashing‖

◦ Typically 64 K of programs (though Flash ROM is much bigger)

◦ Often a separate chip

CMOS

◦ Data

◦ Volatile (kept alive with battery)

◦ Changed via CMOS setup

◦ Typically 128 K of data (though chip size is typically 64 K)

◦ Often on Southbridge

Updating CMOS

• Updated via BIOS program

• Three primary BIOS brands

– American Megatrends (AMI), Award, Phoenix

– To enter setup, press key combination(may be Del, ESC, F1, F2, CTRL-ALT-ESC, CTRL-ALT-INS, CTRL-ALT-Enter, or CTRL-S)

• Main menu

– Access to all submenus

• Clock, hard drives, floppy drives

Normally set to Default or Auto for all

POST, boot order

Use to enable/disable power-saving features

Rarely need to manipulate on today’s PCs

Locks access to CMOS settings◦ Prevents non-techs from changing key settings

If your system keeps resetting

◦ Replace the battery

Common symptoms of low battery

◦ Slow running clock

◦ Clock resetting to January 1st

To clear the CMOS settings, place the shunt on the CMOS jumper

◦ Resets to factory settings

◦ Resets password

CompTIA A+Technician

IT Technician

The power-on self test (POST) is a special program stored on the ROM chip

◦ Initiated when the computer is turned on or is reset

◦ Checks out the system every time the computer boots

To perform this check, the POST ◦ Sends out a standard command that says to all the devices,

―Check yourselves out!‖ ◦ All the standard devices in the computer then run their own

internal diagnostic◦ The POST doesn’t specify what they must check.◦ The quality of the diagnostic is up to the people who made

that particular device. Device — keyboard controller chip runs its

diagnostic and determines that it is not working properly

Communicates errors◦ Beep codes◦ Text errors

A series of beeps—called beep codes—if anything went wrong◦ For bad or missing video :

One long beep followed by three short beeps

End of a successful POST, the PC will produce one or two short beeps, simply to inform you that all is well

If video is determined to be missing or faulty

◦ One long beep followed by three short beeps

If everything checks out

◦ One or two short beeps

If RAM is missing or faulty

◦ Buzzing noise that repeats until power turned off

More complicated beep codes may be found in legacy computers◦ Check motherboard manual for meaning

Any POST errors will display on the screen as a text error

Text error, the problem is usually, but not always, self-explanatory

Far more useful than beep errors because you can simply read the screen to determine the bad device

POST cards are devices that monitor POSTs and report on the hardware that may be causing problems

◦ Turn the PC off, plug in the card, and reboot

◦ POST error codes do not fix the computer – they just tell you where to look

◦ If all else fails, replace the motherboard

POST cards are simple cards that snap into an expansion slot on your system. A small, two-character light-emitting diode (LED) readout on the card indicates what device the POST is currently testing

PC to act dead—no beeps and nothing on the screen◦ POST card, to monitor the POST and identify which

piece of hardware is causing the trouble