Before your operating system loads, something else runs first: the firmware that initialises the hardware and starts the boot process. For decades that was the BIOS. On modern PCs it is UEFI — and the change is more than a new name.
What firmware does at startup
When you power on a PC, firmware runs before any operating system. It checks and initialises the hardware, then hands control to a bootloader that starts the OS. This is the role both BIOS and UEFI fill. UEFI is simply the modern replacement, designed to overcome limits the old BIOS had accumulated over its long life.
The practical differences
Several differences stand out. UEFI supports the GPT partitioning scheme, which removes old size limits and allows much larger boot disks than the BIOS-era MBR scheme could. UEFI generally initialises hardware and boots faster. Its setup interface is often fuller, sometimes graphical, where a classic BIOS was a plain text menu. And UEFI was built to be extensible in ways the rigid old BIOS was not.
The security difference
The most important difference is Secure Boot. UEFI introduced it: a mechanism that checks the bootloader and early boot components against trusted signatures, so the PC only starts software it is meant to. The old BIOS had nothing equivalent. This is why some modern games and anti-cheats can require Secure Boot — it depends on UEFI, and a PC still booting the legacy way cannot offer it.
Why it matters beyond booting
UEFI also relates to hardware identity and trust. It works alongside the TPM and measured-boot features that hardware-rooted security depends on. The move from BIOS to UEFI is part of the same broad shift this site often touches on — trust and identity moving downward into firmware and hardware.
The takeaway
BIOS and UEFI both do the same fundamental job — start the PC — but UEFI is the modern replacement, with larger-disk support, faster boot, a fuller interface, and crucially Secure Boot. That last point is why UEFI is not just trivia: it is the foundation that modern hardware-level security, and some games' requirements, are built on.