Introduction to BIOS Prof. Shamim Ahmad Hakim Deptt. of Computer Science Government Degree College Kulgam J&K-192231 (Class:- 1st Semester)

Computer A device that computes, especially a programmable electronic machine that performs high-speed mathematical or logical operations or that assembles, stores, correlates, or otherwise processes information or one who computes. Computer is a machine for manipulating data according to a list of instructions.

A computer takes many physical forms A computer takes many physical forms. Early electronic computers were the size of a large room, consuming as much power as several hundred modern personal computers. Today, computers can be made small enough to fit into a wrist watch and be powered from a watch battery. Society has come to recognize personal computers and their portable equivalent, the laptop computer, as icons of the information age; they are what most people think of as "a computer".

block diagram of a digital computer

Inside every PC there is BIOS, which stands for Basic Input Output System.  In a nutshell, BIOS is software that interacts between a computer’s hardware and the operating system and software applications.

There are several types of BIOS', ranging from the motherboard ROM BIOS to adapter BIOS' such as video BIOS, drive controller BIOS, network adapter BIOS, SCSI adapter BIOS, etc...

These BIOS' are the lowest level of software in a computer providing a set of small programs or software routines that allow the hardware of a computer to interact with the operating system by a set of standard calls.

I hope to provide a thorough understanding of how the BIOS works and leave you with a better understanding of its interworking. At the same time, I hope to show how complex BIOS is in relation to its relationship with the operating system and the software applications you use every day.

BIOS The Basic Input Output System, usually referred to as BIOS, is software stored on a small memory chip on the motherboard BIOS is sometimes incorrectly referred to as the Basic Integrated Operating System.

What is the BIOS Used For? BIOS instructs the computer on how to perform a number of basic functions such as POST (power on self test) , booting and keyboard control. BIOS is also used to identify and configure the hardware in a computer such as the hard drive, floppy drive , optical drive, CPU, memory etc.

BIOS software is stored on a non-volatile ROM chip on the motherboard BIOS software is stored on a non-volatile ROM chip on the motherboard. It is specifically designed to work with each particular model of computer, interfacing with various devices that make up the complementary chipset of the system.

The Basic Input/output System (BIOS), also known as the system BIOS or ROM BIOS defining a firmware interface (only once programmed at the manufacturing time). The fundamental purposes of the BIOS is to initialize and test the system hardware components, and to load an operating system or other program from a mass memory device.

If the necessary hardware is detected and found to be operating properly, the computer begins to Boot. If the hardware is not detected or is found not to be operating properly, the BIOS issue an error message which may be text on the display screen and/or a series of coded beeps, depending on the nature of the problem. Since POST runs before the computer's video card is activated, it may not be possible to progress to the display screen. The pattern of beeps may be a variable numbers of short beeps or a mixture of long and short beeps, depending on what type of BIOS is installed.

The patterns of beeps contain messages about the nature of the problem detected. For example, if the keyboard is not detected, a particular pattern of beeps will inform you of that fact. An error found in the POST is usually fatal (that is, it causes current program to stop running) and will halt the boot process, since the hardware checked is absolutely essential for the computer's functions.

In modern computer systems, the BIOS contents are stored on an EEPROM Chip so that the contents can be rewritten without removing the chip from the motherboard. This allows BIOS software to be easily upgraded to add new features. EEPROM (electrically erasable programmable ROM) A type of programmable read-only memory (ROM) that can be erased or updated using electrical signals, a process often performed remotely.

BIOS Availability All modern computer motherboards contain BIOS software. BIOS access and configuration on PC systems is independent of any operating system because the BIOS is part of the motherboard hardware. It doesn't matter if a computer is running Windows 7, Windows Vista, Windows XP, Linux, UNIX, or no operating system at all - BIOS functions outside of the operating system environment and is no way dependent upon it.

Here is basic functions of what is happening Power is applied to the computer Bootstrap POST ( power on self test) Booting Looking for the Operating System

Power is applied to the computer When power is applied to the system and all output voltages from the power supply are good, the power supply will generate a power good signal which is received by the motherboard timer.  When the timer receives this signal, it stops forcing a reset signal to the CPU and the CPU begins processing instructions.

Bootstrap The very first instruction performed by a CPU is to read the contents of a specific memory address that is pre-programmed into the CPU.  The code that the processor reads is actually a jump command (JMP) telling the processor where to go in memory to read the BIOS ROM

POST Abbreviated as POST, the Power on Self Test is the initial set of diagnostic tests performed by the computer when powered on. Tests that fail are relayed to the user via the use of POST Codes ,Beep Codes or on-screen POST error messages immediately after the computer powers on.

The POST is handled by the system's BIOS. When power is turned on, POST (Power-On Self-Test) is the diagnostic testing sequence that a computer's basic input / output system (or "starting program") runs to determine if the computer keyboard, random access memory, disk drives, and other hardware are working correctly.

Booting Restarting a Computer or its operating system software. It is of two types Cold booting: when the computer is started after having been switched off. Warm booting: when the operating system alone is restarted (without being switched off) after a system crash or 'freeze.‘

Both types of booting clear out (for the time being) the bugs, bombs, memory conflicts, and other idiosyncrasies of the operating system. The term boot is used to describe the process taken by the computer when turned on, that loads the operating system and prepares the system for use. The first part of the boot process is controlled by BIOS and begins after the POST. Eventually, BIOS hands the boot process over to the master boot code.

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