Firmware

/ˌjuːˈfiːˈaɪ/

noun — "modern firmware interface replacing legacy BIOS."

UEFI, short for Unified Extensible Firmware Interface, is a modern firmware interface for computers that replaces the legacy BIOS. It provides a flexible and extensible environment for bootstrapping operating systems, initializing hardware, and enabling advanced system features. UEFI standardizes the interaction between system firmware and the operating system, supporting large disks, secure boot, and modular firmware components.

Technically, UEFI is stored in non-volatile flash memory on the motherboard and executed by the CPU during the early stages of boot. It supports a richer pre-boot environment, including graphical interfaces, network booting, and runtime services that BIOS lacks. UEFI reads the GUID Partition Table (GPT) to locate bootable partitions, enabling disks larger than 2 TB and more than four primary partitions, addressing MBR limitations.

Core components of UEFI include:

• Boot Manager: Identifies and launches boot loaders or operating systems.
• Device Drivers: Provides low-level control for hardware initialization during pre-boot.
• System Table: Offers runtime services and interfaces for the OS to query firmware capabilities.
• Secure Boot: Ensures that only trusted software is executed during startup, protecting against malware or unauthorized OS loaders.

In workflow terms, UEFI executes as follows: upon power-on, the CPU runs UEFI firmware from flash memory, initializes hardware components, executes POST routines, enumerates devices, reads the GPT to identify bootable partitions, and launches the operating system loader. During runtime, it can provide services such as clock, memory, or firmware update interfaces to the OS.

A simple illustrative pseudo-code for UEFI boot flow:

uefi_init()
check_secure_boot()
enumerate_devices()
boot_partition = find_boot_partition(GPT)
load_bootloader(boot_partition)
transfer_control_to_os()

Conceptually, UEFI is like a modern air traffic control tower: it coordinates and validates all incoming and outgoing operations (hardware initialization and OS boot), ensures security and safety (Secure Boot), and provides rich services to facilitate smooth and reliable system operations beyond the capabilities of the old BIOS.

See BIOS, GUID Partition Table, CPU.

/ˌbaɪˈɒs/

noun — "firmware that initializes and tests hardware at startup."

BIOS, short for Basic Input/Output System, is firmware embedded on a computer’s motherboard that provides the fundamental instructions to initialize hardware components, perform self-tests, and load an operating system from storage. It acts as the bridge between the computer hardware and higher-level software, ensuring that devices are recognized, configured, and accessible before handing control to the operating system.

Technically, BIOS resides in non-volatile memory, traditionally in ROM or flash memory. Upon power-on, the CPU executes the BIOS code starting from a fixed memory address. The BIOS performs the Power-On Self Test (POST), which verifies the integrity and functionality of essential hardware, including CPU, memory modules, storage devices, and peripheral controllers. After verification, it identifies a bootable device and loads its boot sector, such as an MBR or GUID Partition Table, to begin the operating system startup process.

A BIOS typically provides low-level routines for input/output operations, including reading and writing to disk drives, keyboard input, display output, and communication with other peripherals. These routines are exposed to the operating system and applications as a standard interface, allowing software to interact with hardware without requiring device-specific drivers during early boot stages.

Example workflow:

• Power on the system.
• CPU jumps to the BIOS entry point.
• BIOS performs POST to test hardware functionality.
• BIOS initializes system configuration and enumerates devices.
• BIOS locates a bootable device using MBR or GPT and loads the operating system loader into memory.
• Control is transferred to the OS bootloader, completing the startup process.

In modern computing, BIOS has evolved into UEFI (Unified Extensible Firmware Interface), which supports larger drives, more advanced security features, graphical interfaces, and network booting, but maintains backward compatibility with legacy BIOS functionality in many systems.

Conceptually, BIOS is like a stage manager for a theater production: before the main performance (operating system) can start, it ensures all actors (hardware components) are present, functional, and correctly positioned, providing a smooth and coordinated launch.

See MBR, GUID Partition Table, UEFI, CPU.