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11 July 2024  Amanda J. Brook  Senior Product Manager
 

Summary
The article discusses the differences between BIOS (Basic Input/Output System) and UEFI (Unified Extensible Firmware Interface), which are both types of system firmware that play critical roles in the booting process of a computer. It explains that while both BIOS and UEFI provide the necessary instructions for the CPU to start up when a computer is powered on, they differ significantly in terms of functionality and performance. The article aims to highlight these distinctions and examine the scenarios in which one might be preferred over the other.



Table of contents

table iconBoot Procedure
table iconBIOS
table iconUEFI
table iconHow UEFI Replaces and Improves on the BIOS
table iconYou Might Not Need UEFI
table iconConclusion
AMI BIOS 
In the world of computing, two acronyms often come up when discussing system firmware: BIOS and UEFI. These terms stand for Basic Input/Output System and Unified Extensible Firmware Interface, respectively. Both play crucial roles in the booting process of a computer, but they have significant differences in functionality and performance. This article will explore the distinctions between BIOS and UEFI, their roles in the boot procedure, and the scenarios where one might be preferred over the other.

Boot Procedure

To understand BIOS and UEFI, it’s essential to grasp the basic boot procedure of a computer:
1. Power On: When you press the power button, the CPU starts up but needs instructions to proceed since the main memory is empty.
2. Firmware Instructions: The CPU loads instructions from the firmware chip on the motherboard and begins executing them.
3. POST: The firmware performs a Power On Self Test (POST), initializes hardware, detects peripherals, and checks device health.
4. Boot-Loader Search: The firmware scans storage devices for a boot-loader in the first sector of a disk. If found, control is handed over to the boot-loader.
The boot-loader’s responsibility is to load the operating system. For instance, GRUB is a boot-loader capable of loading Unix-like OS and chain-loading Windows OS. The boot-loader loads the kernel into memory, initializes processes, and sets up the system for user interaction.

BIOS

Award BIOS interface 
BIOS, or Basic Input/Output System, is the traditional firmware used in the boot procedure. It is stored on an EPROM (Erasable Programmable Read-Only Memory), allowing for easy updates from the manufacturer. BIOS provides essential functions for reading boot sectors and displaying information on the screen. Users can access BIOS settings during the initial boot phase by pressing keys like del, F2, or F10.

UEFI

uefi_1270 
ASUS UEFI UEFI, or Unified Extensible Firmware Interface, serves the same purpose as BIOS but with several enhancements. Unlike BIOS, UEFI stores all data about initialization and startup in an .efi file on a special partition called the EFI System Partition (ESP) on the hard disk. This partition also contains the boot-loader. UEFI was designed to overcome BIOS limitations, including:
1. Drive Size Support: UEFI supports drive sizes up to 9 zettabytes, compared to BIOS’s 2.2 terabytes.
2. Boot Time: UEFI provides faster boot times.
3. Driver Support: UEFI has discrete driver support, making firmware updates easier.
4. Security: UEFI offers features like Secure Boot, which prevents booting from unauthorized applications, enhancing security but complicating dual-boot scenarios.
5. Operating Modes: UEFI runs in 32-bit or 64-bit mode, allowing for a graphical user interface (GUI) and mouse navigation, unlike BIOS’s 16-bit mode and keyboard-only navigation.

How UEFI Replaces and Improves on the BIOS

UEFI replaces the traditional BIOS on PCs. There’s no way to switch from BIOS to UEFI on an existing PC. You need to buy new hardware that supports and includes UEFI, as new computers do. Most UEFI implementations provide BIOS emulation so you can choose to install and boot old operating systems that expect a BIOS instead of UEFI, so they’re backwards compatible.
This new standard avoids the limitations of the BIOS. The UEFI firmware can boot from drives of 2.2TB or larger—in fact, the theoretical limit is 9.4 zettabytes. That is an appreciable percentage of all of the information on the Internet! That’s because UEFI uses the GPT partitioning scheme instead of MBR. It also boots in a more standardized way, launching EFI executables rather than running code from a drive’s master boot record.
UEFI can run in 32-bit or 64-bit mode and has more addressable address space than BIOS, which means your boot process is faster. It also means that UEFI setup screens can be slicker than BIOS settings screens, including graphics and mouse cursor support. However, this isn’t mandatory. Many PCs still ship with text-mode UEFI settings interfaces that look and work like an old BIOS setup screen.

You Might Not Need UEFI

Despite UEFI’s advantages, there are scenarios where BIOS might be preferable:
1. Simplicity: For beginners who don’t want to mess with firmware settings, BIOS is simpler.
2. Small Drives: If your hard disk or partition is smaller than 2 TB, BIOS suffices.
3. Multiple OS: BIOS allows running multiple operating systems without changing settings, though this poses a security risk.
4. System Information: BIOS provides system information to the OS, useful for 16-bit mode operations without additional code for hardware interaction.
5. Preference: Some users prefer BIOS’s text-based UI and keyboard navigation. UEFI includes a Legacy mode to run everything as if it were BIOS firmware. However, note that Intel announced it would stop supporting traditional BIOS from 2020.

Conclusion

This article provided an overview of the differences between BIOS and UEFI, highlighting their roles in the boot process, their advantages, and scenarios where one might be chosen over the other. Understanding these differences can help you make informed decisions about your computer’s firmware settings and capabilities.
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