What is BIOS?

Basic Input/Output System and furthermore known as the System BIOS, ROM BIOS or PC BIOS is non-unstable firmware used to perform equipment statement amid the booting procedure (control on startup) and to give runtime administrations to working frameworks and programs. The BIOS firmware comes pre-introduced on a PC’s framework load up, and it is the primary programming to run when controlled on.40ad523167dea34b164c1a8462cbec71

Most BIOS usage are particularly intended to work with a specific PC or motherboard display, by interfacing with different gadgets that make up the reciprocal framework chipset. Initially, BIOS firmware was stored in a ROM chip on the PC motherboard.


The BIOS in present-day PCs introduces and tests the framework equipment parts, and loads a boot loader from a mass memory gadget which at that point instates a working framework. In the period of MS-DOS, BIOSthe BIOS gave an equipment reflection layer to the console, show, and other (I/O) gadgets that standardized an interface to application programs and the working framework. Later working frameworks don’t utilize the BIOS subsequent to stacking, rather getting to the equipment segments straightforwardly.


Early Intel processors began at physical address 000FFFF0h. At the point when an green-microchip0441-620x354advanced x86 microchip is reset, it begins in pseudo-16-bit genuine mode, in stating most registers to zero. The code portion enroll is introduced with selector F000h, base FFFF0000h, and breaking point FFFFh, so execution begins at 4 GB short 16 bytes (FFFFFFF0h). The stage rationale maps this address into the framework ROM, reflecting location 000FFFF0h.

On the boot, the framework has quite recently been controlled up or the reset catch was squeezed (“cool boot”), the full power-on individual test (POST) is run. In the event that Ctrl+Alt+Delete was squeezed (“warm boot”), an extraordinary banner esteem is put away in nonvolatile BIOS memory (“CMOS”) before the processor is reset, and after reset the BIOS startup code identifies this banner and does not run the POST. This spares the time generally used to recognize and test all memory.1200px-three_ic_circuit_chips.jpg

The POST checks, distinguish, and instates framework gadgets, for example, the CPU, RAM, hinder and DMA controllers and different parts of the chipset, video display card, console, hard disk drive, optical disc drive and other basic hardware.


The BIOS ROM is altered to the specific maker’s equipment, permitting low-level administrations, (for example, perusing a keystroke or composing a segment of information to diskette) to be given standardized way to programs, including working frameworks. For instance, an IBM PC may have either a monochrome or a color display adapter (utilizing diverse show memory locations and equipment), yet a solitary, standard, BIOS framework call might be conjured to show a character at a predefined position on the screen in content mode or illustrations mode.

The BIOS gives a little library of fundamental information/yield capacities to work peripherals, (for example, the console, simple content and illustrations show capacities et cetera). When utilizing MS-DOS, BIOS administrations could be gotten to by an application program (or by MS-DOS) by executing an INT 13h interfere with a guideline to get to plate capacities, or by executing one of various other recorded BIOS intrude on calls to get to video show, console, tape, and other gadget capacities.

Operating Systems and official programming that are intended to supersede this essential firmware usefulness give substitution programming interfaces to application programming. Applications can likewise give these administrations to themselves. This started even in the 1980s under MS-DOS, when software engineers watched that utilizing the BIOS video administrations for illustrations show was moderate. To expand the speed of screen yield, numerous projects avoided the BIOS and customized the video show equipment straightforwardly. Different illustrations software engineers, especially yet not solely in the demoscene, watched that there were specialized abilities of the PC show connectors that were not bolstered by the IBM BIOS and couldn’t be exploited without evading it. Since the AT-perfect BIOS kept running in Intel genuine mode, working frameworks that kept running in ensured mode on 286 and later processors required equipment gadget drivers good with secured mode task to supplant BIOS administrations.

In present-day PCs running current working frameworks, the BIOS is utilized just amid booting and starting stacking of framework programming. Before the working framework’s first graphical screen is shown, info and yield are regularly taken care of through BIOS. A boot menu, for example, the literary menu of Windows, which enables clients to pick a working framework to boot, to boot into the protected mode, or to utilize the last known great design, is shown through BIOS and gets console contribution through BIOS.

Most current PCs can even now boot and run heritage working frameworks, for example, MS-DOS or DR-DOS that depend vigorously on BIOS for their comfort and plate I/O, giving that the framework has a BIOS or BIOS-perfect firmware, which isn’t really the case with UEFI-based PCs.


Early BIOS versions did not have passwords or boot-device selection options. The BIOS was hard-coded to boot from the floppy drive if that failed, then the hard drive. Access control in early machines was by a physical keylock switch (which was not hard to defeat if the computer case could be opened). Anyone who could switch on the computer could boot it.pcclub-12-biosadvanced

A modern machines BIOS has a setup utility menu-based user interface (UI) which is accessed by pressing a certain key on the keyboard when the PC starts. Usually, the key is pressed for short time during the early startup, for example, “Press F1 to enter CMOS setup”. The actual key depends on specific hardware. Features present in the BIOS setup utility typically include:

  1. Configuring the hardware components, for example, storage controllers are visible to the operating system, manage overclocking the CPU
  2. Setting the system clock
  3. Enable or disable system components by configuration device drivers
  4. Selecting the devices for the boot process, and in which order booting from them d0017381_17254460will be attempted
  5. Setting up passwords, such as a password for giving access to the BIOS interface functions and preventing unknown access users from booting the system from unauthorized portable devices, a password for booting the system, or a hard disk drive password that limits access to that user  and stays even if the hard drive is moved to another computer.


Motherboard BIOS only loads the basic routines to startup the pc.

Drivers of devices are stored on the hard disk drive.

Drivers are directly loaded into RAM and Run from RAM (which is faster).

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