BIOS and CMOS Chapter 5
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)
Historical/Conceptual We Need to Talk
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 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 Northbridge & Southbridge • A chipset is a set of Northbridge and Southbridge chips that work together • Explored in more depth in Chapter 7
Data Flow • Northbridge and Southbridgehave 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 don’t 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)
Talking to the Keyboard • The keyboard talks to the external data bus • Uses the keyboard controller chip (8042)
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
Essentials CompTIA A+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 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 BIOS vs. CMOS
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)
CMOS Setup • Main menu • Access to all submenus
Standard CMOS Features • Clock, hard drives, floppy drives
SoftMenu 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 today’s 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
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
IT Technician CompTIA A+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 We have met the enemy and he is us. - Pogo
Losing CMOS Settings • Common errors • 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
Losing 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
