MELJUN CORTES Computer Organization Lecture Chapter5 BIOS CMOS
Lec post , bios , cmos
Transcript of 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