What is BIOS/UEFI?

What is BIOS/UEFI?

When you press the power button on your computer, the CPU needs instructions to know what to do. It cannot run an operating system yet because the OS is stored on the drive. This is where the BIOS, or Basic Input/Output System, comes in. The BIOS is firmware stored on a chip on your motherboard that initializes your hardware and loads the operating system.

The traditional BIOS has been around since the 1980s. It runs in 16-bit mode, has a simple text-based interface, and can only boot from drives formatted with the Master Boot Record, or MBR, partition scheme. MBR has limitations: it only supports drives up to 2 TB and a maximum of four primary partitions. These limitations led to the development of UEFI.

UEFI, which stands for Unified Extensible Firmware Interface, is the modern replacement for BIOS. It runs in 32-bit or 64-bit mode, has a graphical interface that supports mouse input, and uses the GPT partition scheme instead of MBR. GPT supports drives larger than 2 TB and allows for an unlimited number of partitions. UEFI also boots faster because it initializes hardware in parallel instead of sequentially.

UEFI also supports Secure Boot, a security feature that checks the digital signature of the operating system bootloader before running it. This prevents malicious software from hijacking the boot process. Secure Boot has been controversial because it can make it harder to install alternative operating systems like Linux, but most distributions now support it.

Most modern motherboards still call their firmware settings the BIOS, even though they are actually using UEFI. When you press Delete or F2 during startup to enter the BIOS setup, you are actually entering the UEFI firmware settings. The term BIOS has become generic, like Kleenex for tissues. Whether you call it BIOS or UEFI, it is the first software that runs when you turn on your computer.