Basic Input/Output System

The Basic Input/Output System (BIOS) is a fundamental component of a computer’s system software that initiates hardware operations and provides an interface between the operating system and the hardware. It is stored in a read-only memory (ROM) chip on the motherboard and is responsible for starting the computer, testing hardware components, and loading the operating system into memory.
The BIOS acts as the bridge between the computer’s firmware and software, ensuring that all hardware components function properly before the operating system takes control.

Definition and Purpose

The Basic Input/Output System (BIOS) can be defined as a firmware interface that performs hardware initialisation during the booting process and provides runtime services for the operating system and programs.
Its primary purposes are:

1. System start-up (booting) – Initialises and tests hardware components.
2. Hardware-software communication – Acts as an intermediary between the operating system and hardware devices.
3. Configuration control – Allows users to manage hardware settings via the BIOS Setup Utility.

The BIOS resides in non-volatile memory (such as EEPROM or flash memory), ensuring it remains intact even when the system is powered off.

Historical Background

The concept of BIOS originated with IBM’s first personal computers (IBM PC) in 1981. It was designed to provide a standard interface so that different operating systems and hardware devices could communicate uniformly.
Over time, traditional BIOS has evolved into more advanced firmware systems such as EFI (Extensible Firmware Interface) and UEFI (Unified Extensible Firmware Interface), offering enhanced features, faster boot times, and greater security.

Major Functions of BIOS

The BIOS performs several essential functions in the operation of a computer system. These can be grouped into four key stages:

1. Power-On Self-Test (POST):
   • When the computer is powered on, the BIOS runs diagnostic tests to check the hardware components such as RAM, keyboard, disk drives, and display.
   • If any malfunction is detected, an error message or beep code is generated.
2. Bootstrap Loader:
   • Once POST is completed successfully, the BIOS locates the bootloader on the primary storage device (hard drive, SSD, or optical drive).
   • It then loads the operating system’s kernel into main memory (RAM), initiating system startup.
3. BIOS Drivers and Interrupt Handling:
   • BIOS includes low-level drivers that manage communication between the CPU and peripheral devices such as the keyboard, mouse, and disk drives.
   • It handles interrupt requests (IRQs) that allow hardware components to communicate with the processor efficiently.
4. BIOS Setup Utility:
   • Provides a configuration interface accessible during startup (usually by pressing F2, F10, Delete, or Esc).
   • Users can modify hardware settings such as boot order, clock speed, CPU configuration, and power management.

BIOS Components

The BIOS consists of several distinct modules, each performing specific roles during system operation:

1. POST (Power-On Self-Test): Diagnoses system hardware and ensures all devices are functioning properly before boot.
2. CMOS Setup: Stores system configuration data such as date, time, and boot sequence in a small battery-backed CMOS memory.
3. Bootstrap Loader: Responsible for locating and loading the operating system.
4. BIOS Drivers: Facilitate communication between hardware devices and the operating system.
5. System BIOS Service Routines: Provide low-level routines that software applications can use to interact with hardware devices.

Types of BIOS

There are two main types of firmware interfaces used in modern computing:

1. Legacy BIOS:
   • The traditional BIOS found in older systems.
   • Operates in 16-bit mode, limiting the memory it can access (up to 1 MB).
   • Supports Master Boot Record (MBR) partition tables.
   • Characterised by slower boot times and limited security features.
2. UEFI (Unified Extensible Firmware Interface):
   • The modern replacement for traditional BIOS.
   • Operates in 32-bit or 64-bit mode, allowing access to larger memory and storage devices.
   • Uses GUID Partition Table (GPT) instead of MBR, supporting drives larger than 2 TB.
   • Offers graphical interfaces, faster boot speeds, and enhanced security features like Secure Boot.

BIOS Setup and Configuration

During system startup, the BIOS setup utility allows users to modify hardware settings. Typical configuration options include:

• Boot Order: Determines which storage device the system attempts to boot from first.
• Date and Time: Set and maintain system clock.
• CPU Settings: Adjust frequency, enable/disable hyper-threading or virtualization.
• Memory Configuration: Modify RAM frequency or timings.
• Integrated Peripherals: Enable or disable ports (USB, SATA, LAN).
• Security Settings: Set passwords for BIOS access and drive encryption.
• Power Management: Configure sleep modes and power-saving features.

All configuration data is stored in the CMOS memory, which is powered by a small onboard CMOS battery.

Common BIOS Manufacturers

Several companies develop BIOS firmware for different hardware manufacturers. The most prominent include:

• American Megatrends Inc. (AMI BIOS)
• Phoenix Technologies (Phoenix BIOS)
• Award Software (Award BIOS)
• Insyde Software (InsydeH2O BIOS)

Modern systems often integrate UEFI firmware from these same developers, offering hybrid compatibility.

Importance of BIOS

The BIOS is critical to the functioning of every computer system for several reasons:

• It initiates the boot process and ensures hardware readiness.
• It provides low-level communication between operating systems and hardware.
• It allows users to customise system configuration and troubleshoot issues.
• It supports hardware upgrades by enabling device detection and configuration.

Without the BIOS (or its modern equivalent, UEFI), a computer would be unable to start, load an operating system, or coordinate hardware functionality.

Updating the BIOS

BIOS updates, or flashing, are occasionally released by manufacturers to:

• Fix bugs or hardware compatibility issues.
• Support new CPUs, memory, or storage technologies.
• Improve system performance or add new features.