What is BIOS and UEFI? ~ Fun Programming

When turning on a computer or laptop, you may have noticed a message or logo flashing on the screen before the operating system fully loads. That’s where BIOS or UEFI comes into play. These two terms often pop up when people talk about computer setup, troubleshooting, or even installing a new operating system.

But what exactly are BIOS and UEFI? Are they the same thing, or are they completely different? And why are they important for your computer?

Let’s break it down in a relaxed, easy-to-understand way.

1. What is BIOS?

BIOS stands for Basic Input/Output System. It’s one of the oldest firmware systems that computers have been using since the early PC era.

Think of BIOS as the “bridge” between your computer’s hardware (like the CPU, RAM, hard drive) and the operating system (Windows, Linux, etc.). Without BIOS, your operating system wouldn’t even know where your storage or keyboard is.

Here are some key roles of BIOS:

Booting the system – When you turn on the computer, BIOS runs the POST (Power-On Self Test) process to check if everything is working properly. For example, it checks your RAM, processor, and keyboard.
Loading the operating system – After confirming the hardware is okay, BIOS will search for the device that contains the OS (usually the hard drive or SSD) and load it.
Hardware settings – BIOS allows you to configure basic hardware, like boot order, system time, or enabling/disabling certain features.
Low-level control – It communicates directly with hardware before the OS takes over.

The BIOS interface looks very simple, usually text-based with blue backgrounds and white letters.

2. What is UEFI?

UEFI stands for Unified Extensible Firmware Interface. You can think of it as the modern evolution of BIOS.

As technology advanced, BIOS started to feel outdated and limited. For example, BIOS could only recognize hard drives up to 2 TB, and it wasn’t designed with modern security needs in mind. That’s where UEFI comes in.

Some characteristics of UEFI:

User-friendly interface – Unlike the old BIOS, UEFI often comes with a graphical interface (sometimes even mouse support), making it easier to navigate.
Supports large storage – UEFI can handle disks larger than 2 TB, perfect for modern SSDs and HDDs.
Faster booting – UEFI is optimized to boot the operating system much faster than traditional BIOS.
Secure Boot – A feature that protects your system from malware or unauthorized operating systems by checking digital signatures during boot.
Extensibility – UEFI can support additional drivers and apps, making it more flexible.

Most modern computers and laptops already use UEFI by default, although many still call it "BIOS" for simplicity.

3. BIOS vs UEFI: What’s the Difference?

Although BIOS and UEFI serve the same general purpose (helping your computer start up), there are some significant differences:

Feature	BIOS	UEFI
Release era	1980s	2000s (modern)
Interface	Text-based, keyboard-only	Graphical, often mouse-supported
Storage support	Max 2 TB (MBR partition)	More than 2 TB (GPT partition)
Boot speed	Slower	Faster
Security	Limited	Secure Boot support
Flexibility	Very limited	Supports drivers, network, apps

So, in short: UEFI is like BIOS 2.0 – more modern, faster, and safer.

4. How to Check if Your Computer Uses BIOS or UEFI

Curious about which one your PC or laptop is using? Here’s how you can check:

On Windows:

Press Win + R, type msinfo32, and press Enter.
Look for the line BIOS Mode.
- If it says Legacy, that means it’s BIOS.
- If it says UEFI, well… you already know!

On Linux:

Check the /sys/firmware/efi directory.
If it exists, you’re using UEFI. If not, it’s BIOS.

5. Can You Switch from BIOS to UEFI?

The short answer: Yes, but carefully.

Some older PCs only support BIOS and can’t switch to UEFI. However, many systems that still run BIOS mode (called Legacy Mode) actually support UEFI as well.

To switch:

You need to change the boot mode in your firmware settings.
You may need to reinstall or convert your disk partition style from MBR (Master Boot Record) to GPT (GUID Partition Table).

Warning: Switching modes incorrectly can make your system unbootable. So always back up important data first!

6. Why Should You Care?

You might be wondering: “Do I even need to think about BIOS or UEFI?”

Here’s why it matters:

If you’re installing a new OS, you’ll need to know whether your system is BIOS or UEFI.
If you’re upgrading to a bigger hard drive (more than 2 TB), UEFI is required.
If you care about faster boot times and better security, UEFI is the better option.

So yes, while it works behind the scenes, BIOS/UEFI is an essential piece of your computer puzzle.

7. Final Thoughts

BIOS and UEFI are like the “guardians” that wake up your computer every time you press the power button. Without them, your operating system would have no idea how to talk to your hardware.

BIOS: Old, reliable, but limited.
UEFI: Modern, faster, safer, and more future-proof.

Today, almost all modern laptops and desktops come with UEFI, though many people still call it BIOS out of habit.

So, next time you install Windows, play around with hardware settings, or see the word “UEFI” in your PC specs, you’ll know exactly what it means.

What about you? Have you ever entered your computer’s BIOS/UEFI settings? Or maybe you’ve had an adventure trying to change the boot order?

If yes, share your story—it might help others who are just getting started!

Fun Programming