Bios

BIOSEvans Lampi

University of Zambia

BIOS 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.

BIOS 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.

BIOS AS INTERFACE TO HARDWARE

BIOS AND PC STARTUP Motherboard ROM

Adapter card ROMs (such as that found on a video card)

Loaded into RAM from disk (device drivers)

BIOS ROM Non volatile

Software used to be burned into ROM

Drivers were self-contained, preloaded into memory, and accessible any time the PC was powered on.

ROM AND POST 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 theboot sector from a floppy or hard disk

DRIVERS 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

LIMITATIONS OF ROM BIOS 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

DRIVERS ON BOOT DRIVE 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.

SOFTWARE INTERRUPT 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.

FIRMWARE 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

MODERN IMPLEMENTATION Motherboard BIOS only loads the basic

routines to start up the PC

Drivers are stored on the hard drive

Drivers are loaded into RAM are run from RAM (which is faster)

PC LAYERS

LAYERS SYSTEM purpose of the layered design is to

enable a given OS and applications to run on different hardware

API application programming interface (API)

Consists of the various commands and functions the OS can perform for an applicatione.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.

BIOS AND CMOS RAM BIOS is sometimes confused with CMOS

CMOS is a RTC/NVRAM CMOS stores the configuration file

BIOS setup

MOTHERBOARD ROM BIOSPerforms POST Setup Bootstrap loader BIOS

POST tests computer’s

ProcessorMemoryChipsetvideo adapterdisk controllersdisk drivesKeyboardand other crucial components

SETUP configuration and setup program activated during POST by pressing a key

(e.g. F1) enables configuration of

motherboard and chipset settings date and timePasswordsdisk drivesand other basic system settings

BOOTSTRAP LOADER 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)

VBR 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.

BIOS 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 ROM-based BIOS drivers

ROM CHIP TYPESThe 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

PROM PROGRAMMER

EPROM CHIP

EPROM ERASER

ROM TYPES 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

CHAPTER 5 SECTIONS COVERED BIOS Basics Motherboard ROM BIOS ROM Hardware