The slides describe how the Basic Input Output System (BIOS) functions on a PC

1. Evans Lampi
University of Zambia

2.  BIOS
stands for basic input/output system
 BIOS consists of low-level software that
controls the system hardware.
 BIOS acts as an interface between the
operating system (OS) and the hardware.
 BIOS consists of device drivers, or just
drivers
 BIOS is a link between hardware and
software in a system.

3.  BIOS
consists of software that interfaces the
hardware to the OS
 is
preloaded into read-only memory (or
ROM), and some is loaded into RAM from
disk.

5.  Motherboard
ROM
 Adapter
card ROMs (such as that found on a
video card)
 Loaded
into RAM from disk (device drivers)

6.  Non
volatile
 Software
 Drivers
used to be burned into ROM
were self-contained, preloaded into
memory, and accessible any time the PC was
powered on.

7.  ROM
chip also contained a power-on self test
(POST) program and a bootstrap loader.
 POST
initiates the loading of an OS by
checking for and loading the

boot sector from a floppy or hard disk

8.  Low
level routines
 Originally
all drivers were stored in the BIOS
ROM on the motherboard.
 OS
called on the drivers to interact with the
hardware

9.  What
happens when new hardware is added?
 ROM
is read only and therefore cannot be
changed.
 New
hardware has to come with adapter
cards that have their own BIOS ROMs
 ROM
was programmed to scan a
predetermined area of memory looking for
any adapter card ROMs

10.  Drivers
placed on the boot drive
 Drivers
loaded into RAM during loading of OS
 MS-DOS
startup file (IO.SYS) checked for a
configuration file (called CONFIG.SYS)
 CONFIG.SYS
specified any additional drivers
to load to support new hardware.

11.  Application
through the OS calls to a specific
software interrupt.
 the
interrupt vector table would then route
the call to the specific part of the BIOS
(meaning the specific driver) for the device
being called.

12.  portion
of the BIOS contained in ROM chips
 Found
on the motherboard and in some
adapter cards
 drivers
in nonvolatile ROM remain intact
after power is turned off

13.  Motherboard
BIOS only loads the basic
routines to start up the PC
 Drivers
 Drivers
are stored on the hard drive
are loaded into RAM are run from
RAM (which is faster)

15.  purpose
of the layered design is to enable a
given OS and applications to run on different
hardware

16.  application
programming interface (API)
 Consists
of the various commands and
functions the OS can perform for an
application

e.g.an application can call on the OS to load or
save a file
 Application
does not need to know the
specifics on how to drive particular
hardware.

17.  BIOS
is sometimes confused with CMOS
 CMOS
is a RTC/NVRAM
 CMOS
stores the configuration file
 BIOS
setup

18. Performs
 POST
 Setup
 Bootstrap loader
 BIOS

19.  tests








computer’s
Processor
Memory
Chipset
video adapter
disk controllers
disk drives
Keyboard
and other crucial components

20.  configuration
and setup program
 activated during POST by pressing a key (e.g.
F1)
 enables configuration of





motherboard and chipset settings
date and time
Passwords
disk drives
and other basic system settings

21. A
routine that reads the first physical sector
of various disk drives looking for a valid
master boot record (MBR)
 MBR ends with signature bytes 55AA
 the code is then executed
 MBR program code then reads the first
physical sector called the volume boot
record (VBR)

22.  loads



the first OS startup file, which is
IO.SYS (Windows 9x/Me),
ntldr (Windows XP/2000/NT),
bootmgr (Windows 7/Vista).
 The
OS is then in control and continues the
boot process.

23.  refers
to the collection of actual drivers that
act as a basic interface between the OS and
hardware
 When
running DOS or Windows in Safe
mode, you are running almost solely on ROMbased BIOS drivers

24. The four main types of ROM chips that have
been used in PCs are as follows:
 ROM—Read-only memory
 PROM—Programmable ROM
 EPROM—Erasable PROM
 EEPROM—Electrically erasable PROM, also
sometimes called a flash ROM

28.  ROM
onboard, including the following:
 Video cards—All have an onboard BIOS.
 RAID (Redundant Array of Independent
Disks) cards
 Network card.
 ATA/Serial ATA (SATA) or floppy upgrade
boards
 Y2K boards

29.  BIOS
Basics
 Motherboard ROM BIOS
 ROM Hardware