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

• 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.• This hardware integrated with software is also

referred to as firmware.

BIOS History

• Intel 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)

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.

Cloning• IBM 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.

Clones

• Compaq 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 BIOS

• When you first turn on your PC– 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

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 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.

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 appreas 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

HEX OFFSET Description0000 - 0007 Port addresses, COM1 - COM40008 - 000F Port addresses, LPT1 - LPT40010 - 0011 Installed hardware list0012 initialization flag0013 - 0014 memory size, in Kbytes0015 - 0016 Memory in I/O channel0017 -0018 keyboard status flags0019 alternate key entry storage 001A - 001B Keyboard buffer pointer (head)001C - 001D keyboard buffer pointer (tail)001E - 003D Keyboard typeahead buffer003E - 0048 Diskette data area0049 Current video mode004A - 004B Number of screen columns004C - 004D Regen buffer length, in bytes004E - 004F Regen buffer starting offset0050 - 005F Cursor positions, video pages 1 -80060 Cursor end line0061 Cursor start line0062 Currently displayed video page number0063 - 0064 Active display base address0065 CRT mode register0066 Register for color graphics adapter0067 - 006B Cassette data area006C - 0070 Timer data area

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.