PCs, BIOS vs UEFI

BIOS and UEFI are the firmware interfaces that initialize your computer hardware before your operating system loads. While both serve the same fundamental purpose, UEFI is the modern replacement for legacy BIOS. This guide explains the key differences and how to work with each.

Step 1: What is BIOS?

BIOS (Basic Input/Output System) is an older firmware standard dating back to the 1980s. It performs the Power-On Self Test (POST), initializes hardware, and loads the bootloader.

Uses 16-bit code and runs in real mode
Text-based, keyboard-only interface
MBR (Master Boot Record) boot method
Limited to 2TB boot drives and 4 partitions

Step 2: What is UEFI?

UEFI (Unified Extensible Firmware Interface) is the modern replacement for BIOS, offering a more flexible and secure pre-boot environment.

Supports 64-bit mode, graphical interfaces, and mouse navigation
Faster boot times and better hardware initialization
Uses GPT (GUID Partition Table) — supports drives larger than 2TB
Secure Boot, boot from USB/DVD, network boot, and shell scripts

Step 3: Key Differences

Feature	BIOS	UEFI
Interface	Text-based	Graphical (mouse support)
Boot Disk Limit	2TB (MBR)	More than 2TB (GPT)
Boot Speed	Slower	Faster
Secure Boot	No	Yes

Step 4: Accessing BIOS/UEFI

Press a key like Del, F2, or Esc during startup (varies by motherboard).

Windows 10/11 users can reboot into UEFI:

Settings → Update & Security → Recovery → Restart now → UEFI Firmware Settings

Step 5: Should You Use UEFI?

Most modern systems use UEFI by default.
For dual-booting or legacy software, BIOS compatibility mode may be needed.

Step 6: Converting BIOS to UEFI

Windows users can convert MBR to GPT (backup first):

mbr2gpt /convert /allowfullos

You’ll also need to switch firmware mode from legacy to UEFI in settings.

Next Steps

Explore your system firmware and learn how to configure boot priorities, fan profiles, and XMP settings. Knowing your way around BIOS or UEFI is essential for troubleshooting and performance tuning.