BIOSs

BIOS stands for Basic Input/Output System. It is firmware that provides the first instructions a computer executes when powered on and acts as an interface between the system’s hardware and the operating system. In traditional PC architectures, the BIOS resides in ROM or flash memory on the motherboard and is executed by the CPU during boot.

During the Power-On Self-Test, the BIOS checks essential hardware components, initializes devices such as memory and storage controllers, and prepares the system to hand control to the operating system. It also provides basic software interfaces for keyboard, display, and disk access, allowing early system setup and hardware diagnostics.

After POST, the BIOS reads a boot configuration, typically stored in firmware setup or CMOS, and locates a bootable device according to a boot order. It loads the system’s bootloader or OS kernel into memory and transfers control to it. BIOS settings can be adjusted via a setup utility, often providing options for date and time, boot sequence, device enablement, and security features such as supervisor passwords.

Modern PCs increasingly use UEFI (Unified Extensible Firmware Interface), which replaces or supplements traditional BIOS. UEFI offers 32- or 64-bit code, graphical interfaces, faster boot times, larger boot volumes, and security features like Secure Boot. Many systems provide a Compatibility Support Module to retain legacy BIOS behavior.

Security and maintenance: Because firmware runs with high privileges, malicious firmware can compromise a system. Firmware updates should come from trusted sources, and many vendors provide recovery mechanisms if an update fails. BIOSs continue to play a foundational role in hardware initialization and system boot, even as platforms evolve toward UEFI-based designs.

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