What Is a BIOS?

A BIOS, short for basic input/output system, is the firmware that runs the moment a computer is switched on, before any operating system loads. It lives on a flash memory chip on the motherboard, checks that the hardware works, prepares the processor, memory and devices, and then finds a boot drive and hands control to Windows, Linux or another operating system.

The term dates from 1975, when Gary Kildall used it for the hardware-specific layer of the CP/M operating system. The IBM PC of 1981 put a BIOS in read-only memory, and every PC-compatible computer since has carried one. Firmware vendors such as AMI, Phoenix and Insyde write the core code, and each board maker adapts it to its own hardware.

Strictly, the original BIOS has been replaced. Almost every computer made in the last decade uses UEFI firmware, defined by the UEFI Forum, and Intel ended support for legacy BIOS boot on its client platforms around 2020. People, menus and manuals still call it the BIOS, and this page does the same.

Every power-on follows the same short sequence, usually over in a few seconds.

On a desktop the BIOS is rarely opened. On an industrial or embedded computer that has to start unattended in a cabinet, kiosk or vehicle, a handful of settings decide whether it comes back after a power cut and whether anyone can tamper with it.

The table lists the settings we check most often. Names vary between firmware vendors, but the functions are common to most industrial boards.

Restore on AC power loss is the setting most often missed: with the factory default, an unattended system can stay off after an outage until someone presses the button. Our explainer on what happens during a power cycle covers the behaviour in more detail.

Vehicle computers add power-management settings that a desktop never needs. Ignition sensing turns the computer on when the engine starts and shuts it down cleanly after a set delay when the engine stops, so the battery is not drained and the drive is not corrupted. Our guide to configuring ignition control on vehicle computers walks through the timer choices, and the ignition control explainer covers how the signal is wired.

Rugged systems such as the Premio RCO-6000-RPL combine a 9 to 48 V DC input with ignition management and a PC/Car mode switch, which sets whether the system follows the ignition line or starts like a normal PC. The firmware timers then decide how long it waits before starting and how long it keeps running after the ignition goes off. Our in-vehicle computers carry the same kind of controls.

A BIOS update replaces the firmware on the flash chip with a newer version from the board maker. Updates fix bugs, add support for new processors and memory, and close security holes; several recent processor vulnerabilities were patched through firmware and microcode updates delivered this way.

Updating is also called flashing. It is normally done from a tool in the setup screen, from a USB stick at boot or from the operating system. The one hard rule is not to lose power part-way through, because a half-written image can leave the board unable to start. Many industrial boards carry a backup or dual BIOS that recovers automatically if that happens.

For a fleet, the safer approach is to update only when a release fixes something that affects you, test the new version on one system first, and record the version on every system you ship. Settings can reset to defaults after an update, so check the industrial settings above again afterwards.

We set and record the BIOS settings each system needs, including power-on behaviour, watchdog, boot order and Secure Boot, as part of our standard build, so it starts correctly from its first installation.