BIOS and UEFI
Also known as: basic input/output system, Unified Extensible Firmware Interface, UEFI firmware
BIOS (basic input/output system) and its modern replacement, UEFI (Unified Extensible Firmware Interface), are small programs stored on a chip on the motherboard.
They run the instant you press the power button, check the hardware, and hand control to the operating system. Their settings menus control boot order, security features, and hardware options. While most people never need to open these settings, UEFI features such as Secure Boot quietly protect computers from malware that loads before Windows.
BIOS and UEFI, explained at three levels
At home
BIOS or UEFI is like a building's caretaker who arrives before anyone else each morning. They switch on the power, check that the lights, doors, and elevators work, then unlock the main entrance so the staff can start their day. In a computer, this small program lives on a chip on the motherboard, wakes up the hardware the instant you press the power button, and then hands control to your operating system.
At work
BIOS, and its modern replacement UEFI, is firmware: a small program stored on a chip on each computer's motherboard. It runs the moment a machine powers on, checks the hardware, and starts Windows or another operating system. Businesses care because its settings control security features like Secure Boot, which blocks malware that tries to load before Windows, and because firmware needs patching just like any other software.
At home
When you press the power button, the processor cannot load Windows by itself. It first runs firmware stored on a chip on the motherboard. That firmware tests the hardware, finds the storage drive, and hands control to the operating system's boot loader. The older version was called BIOS, and nearly every modern computer uses UEFI. Pressing a key like F2 or Delete at startup opens its settings, where you can change the boot order or enable features.
At work
UEFI replaced BIOS's 16-bit design with a modern environment that supports GPT partitioning for drives larger than 2 TB, faster startup, network booting, mouse-driven menus and Secure Boot. Secure Boot checks that each boot component is signed by a trusted key before running it, blocking bootkits. Firmware also holds settings for virtualization, the TPM and device security. Manufacturers release firmware updates to fix security flaws and hardware bugs, delivered increasingly through Windows Update.
At home
Updating firmware rewrites the chip that starts your computer. If the power cuts out partway, the computer may not start at all, though many modern boards keep a backup copy to recover from. Updates usually arrive through Windows Update or the manufacturer's app and run during a restart. In my view, always plug a laptop into power before a firmware update and leave it alone until it finishes, because that one simple step avoids most failures.
At work
Firmware is a high-value target because code there runs before the operating system and survives reinstalls, as bootkits such as BlackLotus showed in 2023. Manage settings centrally where vendor tools allow, set supervisor passwords, keep Secure Boot enabled and track firmware versions in your asset inventory. Microsoft's original 2011 Secure Boot certificates began expiring in June 2026, so confirm the replacement 2023 certificates have reached every device. Measured boot with TPM attestation lets device health checks flag tampering.
Real-world examples
At home
Jerome wanted to install Linux from a USB stick. He pressed F12 at startup to open the boot menu and chose the USB drive instead of the hard drive.
At work
Sophie manages devices for a Regina nonprofit. She used the laptop maker's management tool to push a firmware update fixing a security flaw to all 80 laptops.
How it compares
| feature | BIOS | UEFI |
|---|---|---|
| Era | 1970s to 2010s | 2005 onward |
| Interface | Text, keyboard only | Often graphical, mouse support |
| Drive size limit | About 2 TB boot drives | Far larger |
| Secure Boot | No | Yes |
UEFI is the modern successor to BIOS, faster and more secure.
For analysts
I'd include firmware in patch management requirements. It's often missed, and vulnerabilities there can be harder to detect and fix than operating system flaws.
History & origin
Gary Kildall coined the term BIOS for his CP/M operating system in the mid-1970s, and the IBM PC in 1981 made it standard. Compaq's legally 'clean-room' recreation of the IBM BIOS in 1982 opened the door to PC clones, followed by firms such as Phoenix Technologies selling compatible versions. Intel developed EFI in the late 1990s for its Itanium servers, and the industry formed the UEFI Forum in 2005 to standardize it. Windows 8 in 2012 brought UEFI and Secure Boot to mainstream PCs, and Windows 11 in 2021 required UEFI with Secure Boot capability and a TPM 2.0 chip. Microsoft's original 2011 Secure Boot certificates began expiring in 2026, requiring updates to keep older PCs trusted. In my view, firmware is the most important software almost nobody thinks about.