What Is Basic Input/Output System (BIOS)?

May 23, 2024

The Basic Input/Output System (BIOS) is a firmware interface that initializes and tests hardware components during the booting process of a computer. It provides a set of essential routines that enable the operating system to communicate with hardware devices.

What is bios

What Is BIOS?

The Basic Input/Output System (BIOS) is a critical firmware component embedded on a motherboard's ROM chip that is responsible for booting up a computer and managing data flow between the computer's operating system and attached devices. When the computer is powered on, the BIOS performs an initial hardware check, called the Power-On Self Test (POST), to ensure all essential hardware components, such as the processor, memory, and storage devices, are functioning properly.

Following this, the BIOS locates and launches the operating system from a designated storage device, initiating the process that ultimately allows the operating system to take control of the computer. The BIOS also provides a low-level interface for configuring hardware settings, such as system time, boot sequence, and peripheral device settings, ensuring communication and coordination between the hardware and software components of the computer.

A Short History of BIOS

The Basic Input/Output System (BIOS) dates back to the late 1970s. It was first introduced by IBM in 1981 in their initial line of personal computers, the IBM PC. This early version of BIOS was instrumental in standardizing the way computers booted up and interacted with hardware components, providing a consistent interface for the operating system.

Throughout the 1980s and 1990s, BIOS became a cornerstone of PC architecture, evolving to support more complex hardware and advanced features. With the rise of modern computing, the limitations of traditional BIOS led to the development of the Unified Extensible Firmware Interface (UEFI) in the mid-2000s, which offered enhanced security, faster boot times, and greater flexibility. Despite this transition, BIOS remains a foundational technology that paved the way for contemporary computer firmware.

Why Is BIOS Important?

The BIOS is a crucial component of modern computing that links the computer's hardware and operating system. Its importance lies in several key functions that ensure the proper operation and stability of the system. Here are the main reasons why BIOS is important:

  • Boot process initialization. The BIOS is responsible for initiating the boot process. It performs a Power-On Self Test (POST) to check the system's hardware components and ensure they are working correctly before loading the operating system.
  • Hardware configuration. It provides an interface for configuring essential hardware settings, such as system time, boot order, and enabling or disabling specific components, allowing users to customize their system's behavior.
  • Hardware abstraction. The BIOS abstracts hardware details from the operating system, offering a set of standardized routines that facilitate communication between the software and hardware components.
  • System stability and security. By managing low-level system settings and hardware controls, the BIOS helps maintain system stability and security, ensuring that the system runs smoothly and reliably.
  • Firmware updates. BIOS can be updated to fix bugs, enhance performance, and add support for new hardware, extending the lifespan and capabilities of a computer system.

How Does BIOS Work?

When a computer is powered on, the BIOS is the first software to run. It resides on a ROM chip on the motherboard, making it accessible even if the system's hard drive is not functioning. The BIOS performs several crucial functions to prepare the computer for operation:

  1. Power-On Self Test (POST). The BIOS initiates a series of diagnostic tests to verify the proper functioning of essential hardware components like the CPU, RAM, storage devices, and peripherals. If it detects any issues, the BIOS will generate error codes or beep signals to indicate the problem.
  2. Hardware initialization. After the POST, the BIOS initializes the system's hardware components. This includes setting up the CPU, configuring memory, and activating video cards and other peripherals. The BIOS ensures that all components are ready for use by the operating system.
  3. Bootloader. Once the hardware is initialized, the BIOS searches for a bootable device based on the boot order specified in its settings. This could be a hard drive, SSD, CD/DVD drive, or USB device. The BIOS then loads a small program called the bootloader from the selected device into memory.
  4. Bootstrapping the operating system. The bootloader is responsible for loading the operating system into the computer's memory. Once the bootloader is executed, it takes over the process from the BIOS, loading the operating system's kernel and starting its initialization procedures.
  5. System configuration. The BIOS also provides a configuration interface, typically accessed by pressing a specific key (like F2, F10, or DEL) during startup. This interface allows users to adjust system settings, such as the boot order, clock speeds, voltage settings, and enabling or disabling specific hardware components.
  6. Firmware updates and maintenance. Occasionally, the BIOS may need to be updated to support new hardware, fix bugs, or enhance performance. This process is known as flashing the BIOS and typically involves running an update utility provided by the motherboard manufacturer.

Practical Uses of BIOS

The BIOS (Basic Input/Output System) serves several practical uses in managing and configuring a computer system. Here are the key practical uses of BIOS:

  • Boot management. The BIOS controls the boot process, including selecting the boot device and loading the operating system. Users can enter the BIOS setup to change the boot order, enabling booting from different devices like hard drives, SSDs, USB drives, or optical discs.
  • Hardware configuration. BIOS allows users to configure and manage hardware settings. This includes setting system time and date, adjusting CPU clock speeds, configuring RAM timings, and enabling or disabling integrated peripherals such as onboard audio, network adapters, and USB controllers.
  • System diagnostics. During POST, the BIOS performs diagnostics to ensure that all critical hardware components are functioning properly. If issues are detected, the BIOS provides error codes or beep signals to help identify and troubleshoot hardware problems.
  • Firmware updates. BIOS updates, also known as flashing the BIOS, are used to add support for new hardware, fix bugs, and improve system stability and performance. Updating the BIOS can extend the lifespan of a computer by ensuring compatibility with newer components and technologies.
  • Security settings. BIOS includes security features such as setting passwords for system access, enabling or disabling hardware components, and configuring security protocols like Trusted Platform Module (TPM) settings. These features help protect the system from unauthorized access and enhance overall security.
  • Power management. BIOS manages power settings and configurations, including options for power-saving modes, sleep states, and controlling the behavior of system fans and thermal management. Proper power management settings improve energy efficiency and reduce heat generation.
  • Peripheral device management: BIOS handles the initialization and configuration of peripheral devices connected to the computer. This includes configuring input/output ports, setting device priorities, and ensuring proper communication between the operating system and peripheral hardware.
  • Legacy device support. BIOS provides support for older hardware and legacy devices that may not be fully compatible with modern operating systems. This ensures that older peripherals and components can still be used in contemporary systems.

BIOS Types

BIOS has evolved over time, and several types of BIOS are used in different computing environments. Here are the main types of BIOS.

Legacy BIOS

The Legacy BIOS is the traditional firmware interface used in computers since the early days of personal computing. It provides basic functions for booting up the system, performing hardware checks, and loading the operating system. Legacy BIOS operates in 16-bit real mode, which limits its capabilities, particularly with modern hardware and operating systems that require 32-bit or 64-bit support. Despite these limitations, Legacy BIOS remains in use for its simplicity and compatibility with older hardware and software.


The Unified Extensible Firmware Interface (UEFI) is a modern replacement for the traditional BIOS. It offers several advantages over Legacy BIOS, including faster boot times, support for larger hard drives (over 2 TB), and enhanced security features such as Secure Boot. UEFI operates in 32-bit or 64-bit mode, providing a more powerful and flexible interface for interacting with the system firmware. It also includes a graphical user interface, making navigating and configuring system settings easier. UEFI is now the standard firmware interface for most new computers.


Coreboot, formerly known as LinuxBIOS, is an open source project aimed at replacing proprietary BIOS firmware with a minimalistic and flexible solution. Coreboot initializes the hardware and then delegates the remaining tasks to a payload, which can be a bootloader like SeaBIOS, GRUB, or a lightweight operating system. This modular approach allows for faster boot times and greater customization. Coreboot is primarily used in specialized environments, such as embedded systems, servers, and Chromebooks, where performance and flexibility are critical.

Open Firmware

Open Firmware, also known as OpenBoot, is a type of firmware primarily used in Sun Microsystems workstations, servers, and some Apple Macintosh computers. It is based on the Forth programming language and provides a highly flexible and programmable environment for hardware initialization and bootstrapping. Open Firmware supports a wide range of hardware architectures and is known for its portability and extensibility. It allows developers to write scripts for customizing the boot process, making it a powerful tool for advanced users and system administrators.

Intel Boot Guard

Intel Boot Guard is a hardware-based security feature embedded in Intel chipsets that ensures the integrity of the system's firmware. It works by verifying the digital signature of the BIOS or UEFI firmware before it is executed, preventing unauthorized or malicious firmware from compromising the system. This type of BIOS is particularly important in environments where security is a top priority, such as enterprise and government systems. Intel Boot Guard helps protect against firmware-level attacks and ensures that only trusted firmware runs on the system.

BIOS and Security

BIOS plays a crucial role in system security by providing protections that help ensure the integrity and security of the computing environment from the moment the system is powered on. Security features in BIOS include password protection to prevent unauthorized access to BIOS settings, Secure Boot to verify the authenticity of the operating system and prevent the execution of malicious code during the boot process, and Trusted Platform Module (TPM) support for secure cryptographic operations and encryption key storage.

By safeguarding the boot process and hardware configuration, BIOS helps protect against firmware-level attacks, unauthorized hardware changes, and other security threats that could compromise the system before the operating system takes control.

Anastazija is an experienced content writer with knowledge and passion for cloud computing, information technology, and online security. At phoenixNAP, she focuses on answering burning questions about ensuring data robustness and security for all participants in the digital landscape.