BIOS vs UEFI: what they are and what happens when you turn on the computer
Published on 2026-10-19 by frfrand
BIOS y UEFI explicados: cómo arranca una PC, diferencias, Secure Boot, discos GPT y problemas habituales al instalar un sistema.
BIOS and UEFI are firmware technologies that participate in a computer's boot process before Windows or Linux are running. Traditional BIOS comes from an earlier era; UEFI is the modern interface used by most current systems.
If you ever pressed F2 or Delete when turning on a PC to change the boot order, you were already near this part of the system, even if you didn’t know what it was called.
What happens when you press the power button?
Let’s think of a theater. Before the play begins, someone has to turn on the lights, prepare the stage, and open the doors. The actors —the operating system— haven’t appeared yet.
When you turn on the computer, something similar happens: the firmware begins initializing essential components, checks that it can proceed, and looks for a way to load the operating system.
Classic BIOS and UEFI fulfill functions in this stage, but they do not use exactly the same mechanisms.
What was traditional BIOS?
BIOS stands for Basic Input/Output System. For decades, it was the usual way to prepare a PC-compatible machine and begin the boot process.
On systems with traditional BIOS, the startup process usually depended on boot code located in specific parts of a disk, such as the MBR, which then continued loading the necessary components.
It was a suitable solution for its time, but it inherited limitations in compatibility and architecture.
What is UEFI?
UEFI stands for Unified Extensible Firmware Interface. It is not simply a BIOS with a prettier menu: it defines modern interfaces and mechanisms so that the firmware prepares the machine and transfers control to the boot software.
In a typical UEFI installation, the firmware locates a boot program on an EFI System Partition. That application can be a boot manager such as GRUB or the loader used by Windows.
That is why, when installing a system, the chosen boot mode and disk configuration matter. An installation made in UEFI mode may not start if you later switch the machine to legacy mode without preparing the corresponding components.
Are UEFI and GPT the same?
No. UEFI is firmware; GPT is a disk partitioning scheme. Many modern installations use UEFI with GPT, and both concepts appear together, but they describe different things.
It is also not advisable to say that every GPT disk requires UEFI under any circumstance. Special configurations exist. For a beginner, the important thing is to verify that the installer and the machine use a compatible boot mode.
What is Secure Boot?
Secure Boot is a UEFI function that can verify signatures of certain boot components to prevent untrusted pieces from running according to the configured policy.
It is a useful protection against certain attacks before starting the operating system, but it does not mean that the computer is invulnerable, nor that a malicious program within Windows or Linux becomes impossible.
If an installer does not start and someone recommends disabling Secure Boot "just because", it is best to first check if the distribution and its loaders are signed and supported.
How do I know if my computer uses UEFI?
In Windows there is the System Information tool (msinfo32), where the BIOS mode usually appears. In Linux, the presence of the path /sys/firmware/efi usually indicates that the current system booted in UEFI mode.
That describes how the system booted now, which is not exactly the same as listing all possible capabilities of the equipment.
Three frequent confusions
"BIOS and UEFI are the operating system." No. They work before the operating system takes control.
"UEFI makes everything secure." Neither. Secure Boot adds a layer of defense, but you still have to update and protect your programs.
"I can change the boot mode without consequences." Sometimes the system stops booting due to incompatibility between the configured mode and the mode used during installation. Before modifying firmware, back up your data and understand how to recover the system.
Does this matter in a VPS?
Yes, although you might not see it from a panel. On virtual machines, there may be virtual firmware of the BIOS or UEFI type. The provider prepares that layer; you normally interact more with the operating system and services.
In ArduMaker, applications and Linux servers are managed. Understanding the boot sequence helps distinguish an application problem from another that occurs before the system even starts.
In one sentence: BIOS and UEFI set the stage. Then the boot loader comes into play and finally the operating system. If you know the order, diagnosing a failure stops seeming like magic.
Sources: UEFI Forum FAQ · Secure Boot according to Microsoft.