BIOS (Basic Input Output Service) Contains system data used by the ROM BIOS service routines. Serves as a standardized communication interface between the computer’s hardware and the operating system.

BIOS and CMOS in a nutshell In the seconds between the time that you press the power button and the desktop appears on your monitor, your PC goes through a series of ordered steps called the Boot Process. The vital components that drive the boot process are the system ROM, the system basic input/output system (BIOS), and the complementary metal-oxide semiconductor (CMOS) memory chip and setup utility. The system ROM – for read-only memory – is the special memory chip that stores the BIOS programs. System BIOS is the collective name for the hundreds of tiny programs that tell your computer everything from what time it is to what kind of computer it is. The CMOS memory chip and the setup utility enable you to control important aspects of your PC configuration such as the boot device sequence

BIOS Is a small ROM chip on the PC’s motherboard. A basic software program containing all BIOS functions is permanently stored in the ROM. This software functions as a basic operating system. Is responsible for starting the PC. Perform POST (Power-On Self Test) Boot the computer by providing a basic set of instructions. Load the operating system after turning on the computer Provide set-up program for changing BIOS parameters Provide low-level routines for the communications between OS and hardware devices. This hardware integrated with software is also referred to as firmware.

Introduction to BIOS Advantages of storing BIOS in ROM – code and data are readily available during booting – BIOS content are not corrupted by errant applications BIOS hardware components – BIOS ROM PC startup program (POST) – BIOS CMOS memory house the configuration information of individual PC

Introduction to BIOS The BIOS ROM – All BIOS are contained in ROM in old days – BIOS is now located in EEPROM chip erased and rewritten by special programs called flash BIOS BIOS CMOS memory – provide a non-volatile storage for PC’s control information – need very little power to operate – powered by lithium battery

Introduction to BIOS BIOS chip

DOS (Disk Operating System) Fundamentals Consisted of two parts The BIOS itself is one part of the operating system. The other part consists of the operating system program files. – Program files consist of Utilities A kernel that is loaded into the main memory when the computer boots.

Functions of the BIOS When you first turn on your PC. The power supply sends a signal to the components in the system unit. The CPU finds the ROM chips that contains BIOS. The BIOS performs the POST which checks components (e.g. mouse, keyboard connectors and expansion card) The results of the POST are compared with data in the CMOS chip. The BIOS looks for the system files in floppy disk drive and hard disk. The system files and the kernel of the OS load into RAM from hard disk. – Your PC requires information to detect PC components To find the operating system(floppy disk, hard drive, or a CD-ROM) – This information is stored in the BIOS

Flow Chart of BIOS Functions Pass through POST Error Free Plug’n’Play Test Boot Drive Turn on Computer Bootable media found Load boot program Start operating system YES NO Output to Monitor Pass through POST Error Free YE S NO

POST (Power On Self Test) Takes place right after you power on. Contains diagnostic routines for – initializing the hardware and peripherals the video card, the main memory, the processor, the keyboard, etc. – Checking their functions Error message on screen if an error is detected. If monitor cannot be detected, the beep codes are output by the system loud speaker.

The BIOS Boot Process Beep codes – A series of beep: BIOS program encounter problems – One short beep: everything is normal – Errors can be indicated when video screen does not function – Interpret the beep codes by consulting main board menu

The BIOS Boot Process POST Error messages – Error messages are shown on display system – Interpret error messages by consulting owner’s manual

Plug and Play Bios next looks for additional BIOS memory chips – might be on a Plug and Play card such as video card or a SCSI controller. – If present, they run their routines and supplement or replace some functions of the system BIOS. If components no longer match the data stored in the CMOS (i.e. hardware change), message apprears on screen to update.

Plug and Play After all hardware components have been found and checked, Plug and Play goes to work. Interrupts and DMA channels of the plug-in cards in the ISA and PCI buses are queried and distributed. Onboard hardware, located on motherboard and in its ISA/PCI slots, are configured for operation.

Bootstrap Loader BIOS next accesses the first sector of the hard drive, alos termed the boot sector, and starts the “bootstrap loader” – A small program that knows the file structure of the storage medium and can call the operating system’s start routine.

Operating System Kernel Next, the operating system kernel is read into main memory and control of the hardware passes onto the operating system.

An Interpreter In old operating systems (DOS 6.2), the BIOS acts as a mediator (or interface) between the hardware and the software. New operating systems, circumvent the BIOS and communicate directly with the hardware through the appropriate drivers.

BIOS Updating The BIOS is manufactured on FLASH technology. It is easily updated. Previous versions of BIOS were developed on ROM, EPROM, and EEPROM chips.

DOS (Disk Operating System) Fundamentals Consisted of two parts The BIOS itself is one part of the operating system. The other part consists of the operating system program files. – Program files consist of Utilities A kernel that is loaded into the main memory when the computer boots.

Microsoft Kernels Kernel of a Microsoft operating system consists of – Msdos.sys – Io.sys MSDOS.sys controls the keyboard input and the screen output. IO.sys communicates with the BIOS and contains the actual program code of the operating system and a process control for the hardware.

BIOS Data Area, at Segment 0040h

Other BIOS chips in Your PC They have the same functionality as the system BIOS – Control the corresponding device Contain software similar to the system BIOS. Manufactured with FLASH technology to be upgraded easily.

Video BIOS-ROM Contains the basic data – Initialization routines – BIOS functions – Character sets Initializes the registers of the VGA chip Sets the interrupt vectors for the interrupts

Video Interrupt There is a software interrupt that permits the software to communicate with the video card. INT 10h Can access the registers through it Can control the mode, character input/output, and read/write pixels.

Configuring the BIOS Setup program interfaces 1.Hit a particular key or key combination at a right time to enter the BIOS setup utility

Configuring the BIOS Setup program interfaces 2. A BIOS setup screen is displayed.

Configuring the BIOS Typical key control – Incorrect settings of BIOS may lead to system halt – Quit the setup without saving changes if we are not sure about the changed settings – Boot sequence control the order in which BIOS looks for an OS on start-up usual sequence: floppy disk  hard disk  CD-ROM

Configuring the BIOS Typical key control – Performance tuning through BIOS settings BIOS settings are responsible for how the chipset is controlled. Chipset is the key to the overall system performance BIOS parameters: – Choose the optimal bus speed settings – Enable the CPU’s internal cache – External cache memory – Enable system BIOS shadowing – Quick power-on self test – Update the BIOS

BIOS information CMOS information

CMOS or Setup Option to use this program is early in the boot cycle – long before system loads Operating System Different key(s) to enter different Setups You should only get to Setup on purpose Program stored in BIOS, but only edits data in CMOS First CMOS was set of switches!

Who makes BIOS? Award Software Phoenix Technologies AMI – American Megatrends Inc. They write BIOS with lots of options; motherboard maker picks sections to be used Long gone are IBM’s patents on BIOS Same parent company

Setup Lots of screens and subscreens You don’t need to know about all settings on all screens Motherboard book is mildly helpful on some options You should know generally where things can be found

Date and Time and … Usually on the first screen, or first menu choice Lets you set Date, Time, floppy present (will autodetect it), memory count, hard drive(s) present (again, autodetected)

Here is where you set the boot order

When adding a modem, you might want to turn both of these off.

New CMOS Did you notice the “High Performance” option? Did you see the “Setup Defaults” option? BIOS can “talk” to hard disk drive and get all the information it needs. About the worst that happens today is the need to reset date and time.

The Three-In-One We have BIOS that stores code and access program to CMOS We have CMOS that stores changeable information about our system We have RTC (Real Time Clock) that keeps track of date and time All three are now rolled into one chip

Easy way to spot this chip is by the shinny label

About that Battery Should last 5 to 10 years You can find them at Savon even If your system forgets date and/or time, it’s time to replace the battery

More Battery Sometimes we WANT to reset CMOS: – A forgotten password – Too aggressive overclocking – Incorrect low-level settings on some screen Either move the jumper, or pull the battery Do either for about 10 seconds If you are to pull battery, make sure you unplug system too

10