Difference Between BIOS and UEFI: Understanding the Evolution of Computer Firmware

Introduction

Every computer needs a firmware interface that acts as a bridge between its hardware and the operating system.
For decades, this role was played by BIOS (Basic Input/Output System) — a simple, text-based firmware that initializes the hardware during startup.

However, as technology advanced, BIOS became limited in speed, storage support, and flexibility.
To overcome these shortcomings, UEFI (Unified Extensible Firmware Interface) was introduced as its modern replacement.

In this article, we’ll explore the key differences between BIOS and UEFI, their functions, advantages, and why modern systems prefer UEFI over traditional BIOS.

What Is BIOS?

🔹 Definition

BIOS stands for Basic Input/Output System.
It’s a firmware program stored on a small chip on the motherboard that initializes your computer’s hardware during the boot process and hands control over to the operating system.

🔹 How BIOS Works

When you press the power button:

1. BIOS performs the POST (Power-On Self-Test) to check memory, CPU, and hardware.
2. It finds a bootable device (like a hard drive or USB).
3. BIOS loads the bootloader from the Master Boot Record (MBR).
4. The operating system then starts.

🔹 Key Features

• Text-based user interface (keyboard-only navigation).
• Uses 16-bit processor mode.
• Limited to 2.2 TB disks (due to MBR).
• Supports Legacy Boot mode.

What Is UEFI?

🔹 Definition

UEFI stands for Unified Extensible Firmware Interface.
It’s a modern firmware interface that replaces the traditional BIOS, offering faster boot times, larger drive support, enhanced security, and a more flexible architecture.

🔹 How UEFI Works

UEFI initializes hardware much like BIOS but uses GUID Partition Table (GPT) instead of MBR.
It then launches the OS directly from the EFI System Partition (ESP) — a special area on the disk containing bootloaders and drivers.

🔹 Key Features

• Graphical interface (mouse and keyboard support).
• Uses 32-bit or 64-bit mode for faster operations.
• Supports disks larger than 2 TB.
• Includes Secure Boot for malware protection.
• Compatible with GPT partition scheme.

BIOS vs UEFI: Key Differences

Boot Process Comparison

🔸 BIOS Boot Process

1. Power ON → POST (hardware check).
2. BIOS finds and loads bootloader from MBR.
3. Bootloader launches the OS kernel.

This method depends heavily on the physical disk structure (MBR).

🔸 UEFI Boot Process

1. Power ON → UEFI initializes hardware.
2. It reads the EFI System Partition (ESP).
3. Loads the OS boot manager (stored as a file, e.g., bootmgfw.efi for Windows).

This process is faster, secure, and supports multiple OS entries — ideal for dual-boot systems.

Security: BIOS vs UEFI

UEFI’s Secure Boot is one of the most significant improvements.
It ensures that only trusted software (signed by verified keys) can run during startup — preventing rootkits and low-level malware infections.

Performance: Boot and Operation Speed

UEFI significantly improves boot speed and shutdown time compared to BIOS.
It can initialize devices in parallel, while BIOS initializes one at a time.

• BIOS Boot Time: Slower (sequential initialization)
• UEFI Boot Time: Faster (parallel initialization)

Also, UEFI can resume from hibernation or sleep modes faster because of its optimized firmware routines.

Compatibility and OS Support

Modern OSes like Windows 11 require UEFI Secure Boot and TPM 2.0 for installation — marking the complete transition away from BIOS.

Storage and Partition Support

BIOS (MBR)

• Supports only 4 primary partitions.
• Max disk size: 2.2 TB.
• No data redundancy.

UEFI (GPT)

• Supports 128 partitions in Windows.
• Can handle drives larger than 2 TB.
• Uses CRC32 checksum and backup headers for recovery.

👉 UEFI + GPT is ideal for SSDs, NVMe drives, and large storage arrays.

Upgradability and Flexibility

Unlike BIOS, which is stored in ROM and rarely updated, UEFI can be upgraded easily by manufacturers through firmware updates.

• UEFI supports network-based booting, remote management, and custom drivers.
• BIOS is fixed and limited to predefined hardware functions.

Pros and Cons Summary

How to Check Whether Your System Uses BIOS or UEFI

🔹 On Windows:

1. Press Windows + R → Type msinfo32 → Enter.
2. Look for BIOS Mode → It will show Legacy or UEFI.

🔹 On Linux:

Run the command:

ls /sys/firmware/efi

If the folder exists, you’re using UEFI.

Transition from BIOS to UEFI

The shift from BIOS to UEFI has been gradual.
Initially, UEFI coexisted with BIOS in Compatibility Support Mode (CSM) to support older OSes.
However, as of 2025, most systems and motherboards ship with UEFI-only firmware, marking the end of traditional BIOS after more than four decades.

Final Verdict: Why UEFI Is the Future

UEFI is faster, safer, and more flexible than BIOS.
With features like Secure Boot, GPT partitioning, and modern OS support, it has become the standard firmware for all modern PCs.

If you are installing or upgrading a system in 2025, UEFI is the clear choice — offering better performance, scalability, and security.