UEFI vs BIOS | What Are The Key Differences? – Quick Explanation

UEFI vs BIOS is a common topic for new users when they purchase a new PC. Many users when they upgrade their PCs don’t know what firmware is running. Is it BIOS or UEFI? Or they just completely misunderstood these terms.

BIOS and UEFI are the common acronyms in this PC world. These are the programs that enable your computer to start in the first place. UEFI or Unified Extensible Firmware Interface and BIOS or Basic Input/Output System are doing the same thing but differently.

Both two start up the CPU, load all the peripherals (keyboard, mouse, pen drives, etc), look for bootloaders, and start up the operating system. But if they do the same thing then what are the differences? I’m glad you asked.

Even though they look similar there are a lot of things going under the hood.


BIOS stands for Basic Input/Output System, a legacy firmware used to use to activate the boot procedure. The American computer scientist Gary Kildall first introduced BIOS in the CP/M operating system in 1975. The BIOS firmware comes pre-installed on every modern motherboard.

This is the first software to run when the computer is turned on. It initializes all the connected hardware, checks for errors, and gives a POST (power-on self-test) screen. After passing the POST, the BIOS handover the computer to the Operating System.


UEFI or Unified Extensible Firmware Interface is a modern firmware developed to increase the BIOS functionalities. There is no way of upgrading existing hardware from BIOS to UEFI. You have to purchase new hardware that supports UEFI. If you have hardware from 2007 or later, you may have support for UEFI. Most of the modern hardware is shipped with UEFI with legacy BIOS support.

So if you want BIOS for your operating system, you can do that by activating CSM (Compatibility Support Module) from the UEFI settings.

The BIOS and the UEFI are both doing the same thing. But UEFI has wider features and functionalities. UEFI can run in 32-bit or 64-bit mode whereas BIOS only runs in 16-bit mode. That means UEFI has more addressable addresses than BIOS. This helps UEFI to initialize the boot process much faster.


When you turn on your computer, it has nothing to do. Because the RAM is empty. So the chip manufacturers set some pre-defined instructions to work with. Whenever you turn on your computer, the BIOS or UEFI initiates the following tasks.

  • POST (Power-on self-test)
  • Initialize all the available hardware and check for errors.
  • Load and execute the first stage of the operating system boot sequence.

BIOS stores all its configuration on firmware whereas UEFI stores all the initialization data on a .efi file. This EFI file is stored on a special partition called EFI System Partition (ESP) on the hard disk. This ESP partition also contains the OS bootloader.

The BIOS is old and has serious limitations. Though BIOS has evolved and improved over time to some extent but not like other PC technologies.

It uses 16-bit processor mode and 1 MB of space to initialize all the hardware resulting slow boot process. Hard drives of more than 2 TB are common these days. It cannot boot from a drive of more than 2 TB. This is how BIOS’s Master Boot Record or MBR works.

MBR does not support more than 4 primary partitions and has many security issues too. That’s why GPT is developed to address these issues. GPT or GUID Partition Table is the standard for the layout of partition tables of a physical computer storage device such as HDD or SSD. It’s a part of the UEFI.

UEFI uses 32-bit or 64-bit mode and has more addressable address space than BIOS resulting faster boot process. It also supports storage larger than 2 TB and technically up to 9.4 zettabytes. Thanks to the GPT partition scheme.

UEFI setup screen has a more beautiful user interface and mouse support than BIOS’s text-based setup screen. Although many PCs come with text-based UEFI that does not have slick UI or mouse support and looks just like old BIOS.

UEFI comes with other features like Secure Boot and networking features for remote troubleshooting and configuration. Some UEFI has legacy BIOS support for backward compatibility. To use legacy BIOS on a UEFI-based PC, you need to enable CSM or Compatibility Support Module from the settings menu.


There you have it. A brief overview of UEFI vs BIOS and how they work. I hope this blog post will help you to understand the basics of these two firmware. If you have any questions or want to share your thoughts, please comment down below. I will be happy to hear from you. Till then, have a great day.

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