Suleiman Mohammed (mcpn,mncs)
BIOS and CMOS Instructor Suleiman Mohammed (mcpn,mncs) Institute of Computing & ICT, Ahmadu Bello University, Zaria. Overview In this chapter, you will learn to
Explain the function of BIOS Distinguish among various CMOS setup utility options Describe option ROM and device drivers Troubleshoot the power-on self test (POST) Bridge Introduction Data flows through the computer
Between CPU and RAM Between CPU and video Between CPU and other devices Bridges are used to connect the pieces Northbridge Bridge closest to the CPU Southbridge The farther bridge Northbridge & Southbridge
A chipset is a set of Northbridge and Southbridge chips that work together Northbridge Chip or chips that connect the CPU to video and/or memory Southbridge Handles all of the inputs and outputs to the many devices in the PC Chipset makers rarely use the terms Northbridge and Southbridge anymore, but because most modern chipsets consist of only two or three chips with basically the same functions, techs continue to use the terms. Explored in more depth in Chapter 7 Data Flow Northbridge and Southbridge have connectivity with all devices Not the same in all systems Chipset Northbridge Southbridge Basic Input/Output System (BIOS)
Bridges connect the devices But without a program, they dont know how to communicate A special kind of program is required to enable the CPU to talk to other devices A Flash ROM chip stores these programs These programs are collectively known as the basic input/output service (BIOS) The ROM chip on the motherboard that holds the system BIOS is called the system ROM, or ROM BIOS. Talking to the Keyboard
The keyboard talks to the external data bus Uses the keyboard controller chip (8042) The Southbridge chip handles the keyboard interface, acting as the keyboard controller chip among its many other functions. Manufacturers today choose a specific chipset, rather than an individual keyboard controller. Keyboard controller chip
BIOS Each program is called a service Programs stored on Flash ROM chips are known as firmware Programs stored on erasable media are called software Keyboard controller chip Discussion Point Software and firmware Programs that typically reside in RAM or on other erasable media are called software, while programs that reside in ROM are called firmware. Essentials CMOS CMOS Separate chip from ROM BIOS Volatile (kept alive by battery)
Stores only changeable data Not programs Acts as clock to keep data current Customizable via SETUP program Often on Southbridge BIOS vs. CMOS CMOS BIOS Data Programs
Volatile (kept alive with battery) Changed via CMOS setup Typically 128 K of data (though chip size is typically 64 K) 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 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) BIOS manufacturers In 1998, Phoenix and Award merged as Phoenix. However, Phoenix still markets Phoenix and Award BIOS separately. CMOS Setup Main menu Access to all submenus Note
Not all Award CMOS setups will have the same pages as those listed here. Standard CMOS Features
Clock, hard drives, floppy drives Soft Menu Setup Normally set to Default or Auto for all Advanced Features POST, boot order Power Management Use to enable/disable power-saving features PnP/PCI Rarely need to manipulate on todays PCs Set Password Locks access to CMOS settings
Prevents non-techs from changing key settings Option ROM and Device Drivers BYOB Computer makers could not predict all the new types of hardware
Ways to bring your own BIOS (BYOB) were invented: Option ROM is a BIOS chip embedded on the adapter card itself (i.e., video cards) Most new hardware devices use device drivers to tell the BIOS how to talk to the CPU Most devices with onboard BIOS use it only for internal needs (internal function) and use a device driver to talk to the CPU Device Drivers A device driver is a file that contains the BIOS commands necessary to communicate with the devices they support Loaded into RAM when the system boots All devices come with their own device drivers Device drivers have one big limitationthey dont start until the operating system starts them. Some devices still use ROM BIOS to enable them to boot the system. BIOS, BIOS, Everywhere All hardware needs a program to allow CPU to communicate with it Could be on motherboard ROM Could be on PC card ROM Could be loaded via a driver Could be loaded into RAM at boot Power-On Self Test (POST)
IT Technician Power-On Self Test (POST) Power-On Self Test (POST)
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 Communicates errors Beep codes Text errors Beep Codes 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 Text-Based Error Message POST Cards 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 The Boot Process The CPU is the first component initialized when the computer is turned on It reads a special wire called power good once the power supply provides the proper voltage to the CPU Every CPU has a built-in memory address with the first line of the POST program on the system ROM The Boot Process The last BIOS function called by POST is the bootstrap loader The bootstrap loader loads the operating system from the boot sector Searches the floppy, CD-ROM, or the hard drive Boot order set in CMOS The bootstrap loader generates an error if it cannot find the boot sector on the bootable disk Care and Feeding of CMOS/BIOS
Instructor Tip Pogo once said We have met the enemy and he is us. English grammar aside, the real message is that we are often our own worst enemy. Working with BIOS and CMOS is a great example. It often works fine until we start changing things. A sound troubleshooting principle is to do only one thing at a time, and if it doesnt resolve the problem, put it back the way it was. The tech that makes change after change without normalizing the system inserts new problems. Losing CMOS Settings Common errors Common reasons for losing CMOS data
CMOS configuration mismatch CMOS date/time not set No boot device available CMOS battery state low Common reasons for losing CMOS data Jiggling the battery while doing other work Dirt on the motherboard Electrical surges Faulty power supplies Chip creep Loosing CMOS Settings If your system keeps resetting
Replace the battery Common symptoms of low battery Slow running clock Clock resetting to January 1st Clearing CMOS Settings
To clear the CMOS settings, place the shunt on the CMOS jumper Resets to factory settings Resets password Flashing ROM 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 Thank You