BIOS(Basic Input Output Service)

Contains system data used by the ROM BIOS service routines.

Serves as a standardized communication interface between the computers hardware and the operating system.

BIOSIs a small ROM chip on the PCs 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.This hardware integrated with software is also referred to as firmware.

BIOS HistoryIntel developed the 8086 and 8088 in the end of the 70s.IBM decided to make an affordable computer out of the 8088.Microsoft created the operating system (DOS).

DOS(Disk Operating System) FundamentalsConsisted of two partsThe BIOS itself is one part of the operating system.The other part consists of the operating system program files.Program files consist of UtilitiesA kernel that is loaded into the main memory when the computer boots.

CloningIBM introduced the complete PC with the operating system in 1981.IBM owned copyrights to the BIOS. IBM published all the assembly language source code for the IBM PC/XT BIOS.Peter Norton wrote the landmark book Inside the IBM-PC.Microsoft made DOS available to other licensees.

ClonesCompaq developed a BIOS by 1983. Also introduced their own PC.Phoenix Technologies released a BIOS package (IBM-compatible BIOS and a version of DOS).Manufacturers of today, such as AMI, Award and MR-BIOS, all developed their own source code for an IBM-compatible BIOS.

Functions of the BIOSWhen you first turn on your PCYour PC requires information to detect PC componentsTo find the operating system(floppy disk, hard drive, or a CD-ROM)This information is stored in the BIOS

Flow Chart of BIOS FunctionsPass through POST Error Free

PlugnPlay

Test Boot Drive

Turn on Computer

Bootable media found

Load boot program

Start operating system

YES

NO

NO

Output to Monitor

Pass through POST Error Free

Pass through POST Error Free

Pass through POST Error Free

YES

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 functionsError message on screen if an error is detected. If monitor cannot be detected, the beep codes are output by the system loud speaker.

Plug and PlayBios 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 appreas on screen to update.

Plug and PlayAfter 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 LoaderBIOS next accesses the first sector of the hard drive, alos termed the boot sector, and starts the bootstrap loaderA small program that knows the file structure of the storage medium and can call the operating systems start routine.

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

An InterpreterIn 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 UpdatingThe 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) FundamentalsConsisted of two partsThe BIOS itself is one part of the operating system.The other part consists of the operating system program files.Program files consist of UtilitiesA kernel that is loaded into the main memory when the computer boots.

Microsoft KernelsKernel of a Microsoft operating system consists ofMsdos.sysIo.sysMSDOS.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

Sheet1

HEX OFFSETDescription

0000 - 0007Port addresses, COM1 - COM4

0008 - 000FPort addresses, LPT1 - LPT4

0010 - 0011Installed hardware list

0012initialization flag

0013 - 0014memory size, in Kbytes

0015 - 0016Memory in I/O channel

0017 -0018keyboard status flags

0019alternate key entry storage

001A - 001BKeyboard buffer pointer (head)

001C - 001Dkeyboard buffer pointer (tail)

001E - 003DKeyboard typeahead buffer

003E - 0048Diskette data area

0049Current video mode

004A - 004BNumber of screen columns

004C - 004DRegen buffer length, in bytes

004E - 004FRegen buffer starting offset

0050 - 005FCursor positions, video pages 1 -8

0060Cursor end line

0061Cursor start line

0062Currently displayed video page number

0063 - 0064Active display base address

0065CRT mode register

0066Register for color graphics adapter

0067 - 006BCassette data area

006C - 0070Timer data area

Sheet2

Sheet3

Other BIOS chips in Your PCThey have the same functionality as the system BIOSControl the corresponding deviceContain software similar to the system BIOS.Manufactured with FLASH technology to be upgraded easily.

Video BIOS-ROMContains the basic dataInitialization routinesBIOS functionsCharacter setsInitializes the registers of the VGA chipSets the interrupt vectors for the interrupts

Video InterruptThere is a software interrupt that permits the software to communicate with the video card.INT 10hCan access the registers through itCan control the mode, character input/output, and read/write pixels.