Transcript BIOS (Basic Input Output Service)

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
Turn on Computer
Pass through POST Error Free
YE
S
Plug’n’Play
N
O
Output to Monitor
Pass through POST Error Free
Test Boot Drive
Bootable media found
Load boot program
Start operating system
N
O
Pass through POST Error Free
YE
S
Pass through POST Error Free
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
0000 - 0007
0008 - 000F
0010 - 0011
0012
0013 - 0014
0015 - 0016
0017 -0018
0019
001A - 001B
001C - 001D
001E - 003D
003E - 0048
0049
004A - 004B
004C - 004D
004E - 004F
0050 - 005F
0060
0061
0062
0063 - 0064
0065
0066
0067 - 006B
006C - 0070
Description
Port addresses, COM1 - COM4
Port addresses, LPT1 - LPT4
Installed hardware list
initialization flag
memory size, in Kbytes
Memory in I/O channel
keyboard status flags
alternate key entry storage
Keyboard buffer pointer (head)
keyboard buffer pointer (tail)
Keyboard typeahead buffer
Diskette data area
Current video mode
Number of screen columns
Regen buffer length, in bytes
Regen buffer starting offset
Cursor positions, video pages 1 -8
Cursor end line
Cursor start line
Currently displayed video page number
Active display base address
CRT mode register
Register for color graphics adapter
Cassette data area
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.