What is BIOS (Basic Input/Output System)?

BIOS (Basic Input/Output System) is a program recorded on a chip on the motherboard, in particular, EEPROM (Electrically Erasable Programmable Read-Only Memory) type.

What is BIOS (Basic Input/Output System)?

BIOS Functions

BIOS is an application that finds, recognizes and configures all devices of a Motherboard (MB) required to load the Operating System into RAM. It provides a low level of communication, operation, and system hardware configuration, at least that operates the keyboard and provides a basic output (emitting standard beeps from the computer speaker) during startup.

It is usually written in Assembly Language. The first term appeared in the CP/M operating system and describes the portion of CP/M that is executed at startup and is connected directly to the hardware. Most MS-DOS versions have a file called IBMBIO.COM or IO.SYS, which is similar to CP/M.

It is a basic input/output system that is typically not noticed by the end-users of computers. It is responsible for finding the operating system and loading it into RAM. It has a hardware and a software component, the second provides a general text interface (SETUP) that allows you to configure various hardware options such as the clock installed on the PC or from which storage devices the operating system will start.

At least it manages the computer keyboard and even provides a fairly basic output in the form of sounds from the built-in speaker on the motherboard when there is a fault such as a device that fails or needs to be connected.

These error messages are used by technicians to find solutions when installing or repairing equipment. This is located in the EEPROM memory. It is a firmware type program.

It is an essential part of the hardware that is partially configurable and where information flow processes are controlled on the computer bus, between the operating system and other peripherals. It also includes the configuration of very important aspects of the machine.

The BIOS system of a standard computer actually performs four independent functions:

  1. Hardware Inventory and Test Program (Power On Self Test).
  2. The first software installation.
  3. Initialization of hardware devices that require; installing some basic software and starting the operating system.
  4. Support for certain system hardware devices.


To access the configuration program, usually called Setup, you need to do this by pressing one or more keys during computer startup.

In general, it is usually the Delete key, but this varies depending on card types and laptops. The other keys used are F1, Esc, F2, or a combination of keys, just to consult your motherboard’s manual or pay attention to the initial splash screen for complete understanding, because a message usually appears at the bottom: It looks like this: Press DEL to enter Setup.

The Setup is usually in excellent English, and terms that are not really simple also appear, if you don’t know what you are doing, consult the manual or a specialist, otherwise, you will encounter problems. Although they have different names, there are some partitions common to all types of BIOS. A classification can be:

  • Basic parameter configuration – Standard CMOS Setup.
  • BIOS Options – BIOS Features, Advanced Setup.
  • Advanced configuration and chipset – Chipset features.
  • Password, peripherals, hard drives.


Normally, this software is saved to a read-only memory chip ROM on the motherboard called memory ROM BIOS. This ensures that it will not be lost when shutting down the System and its performance will not depend on the presence or proper operation of any disc, so it will always be available.

The latter is important because it provides the first start of the equipment without requiring any external resources. From the first days of the computer’s lifetime, the ROM-BIOS gave problems with existing hardware, because technical improvements were constant; it was necessary to increase the capacities of devices connected to the disk and equipment.

This required new BIOSs needed to replace the motherboard or at least replace the integrated one containing the ROM BIOS in later models. Rewritable memories such as EPROM (Erasable programmable read-only memory) and EEPROM (Electrically erasable programmable read-only memory) were started to solve the problem.

Currently, a type of non-volatile flash memory (Flash BIOS) is used, which can be rewritten without any special deletion or recorder and allows it to be updated very conveniently.

Usually, it is only necessary to download the appropriate version from the internet (usually from the motherboard manufacturer’s site) and follow the instructions that come with the program.

Since the BIOS is constantly used in normal PC operation and RAM is accessed faster than ROM, many manufacturers require that the BIOS ROM content be copied to RAM as part of the boot process. first. This is known as Shadowing and has the effect of speeding up system performance. The BIOS version loaded into RAM is called shadow BIOS.

Naturally, this requires a realignment of the cutting vectors, so they point to new locations in RAM. The most modern BIOS is called PnP BIOS or PnP compatible BIOS. This means that they are intended to address Microsoft’s “Plug and Play” PnP standard.

IRQ is a technology that allows it to identify any hardware device connected and to sign the necessary resources without conflict with the rest. Before this technology, the addition of new devices was a real headache, given the resource shortage expected by PC designers. For example, well-known IRQs and port address conflicts.

Firmware on Adapter Cards

A system may contain various chips with BIOS firmware. In addition to the boot BIOS on the hard drive and motherboard.

Manufacturer Market

The vast majority of PC motherboard vendors hand over the production of the BIOS and a number of tools to third parties.

These are known as independent vendors or IBVs. Motherboard manufacturers then customize this BIOS to their hardware. For this reason, updates are often received directly from the motherboard manufacturer.

The manufacturer may post firmware updates through the website, but poor compatibility with the hardware can become completely useless by causing a bug that spreads across the motherboard. The main providers are American Megatrends (AMI), General Software, Insyde Software and Phoenix Technologies (acquired Award Software International in 1998).

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