UEFI (Unified Extensible Firmware Interface) is the modern replacement for the old BIOS. It's the firmware that runs when you press the power button — checking the parts, then starting Windows — just like the BIOS did, but faster and more capable.
How it differs from the old BIOS
- Faster boot and a more reliable start-up.
- Supports large drives (beyond 2 TB) that the old BIOS couldn't handle.
- A modern setup screen you can drive with a mouse, not just arrow keys.
- Secure Boot, which helps block malware that tries to load before Windows.
Why it matters to you
You won't touch it much. But it's the reason you can plug in a big SSD and have it work, and it's where settings like the boot order and Secure Boot live. If a PC won't start Windows, a UEFI/BIOS setting or a failed drive is often the cause.
"BIOS" and "UEFI" are often used interchangeably now. If you see a "press F2 to enter setup" loop, the PC is failing to find a boot drive — worth a technician if it repeats.