BIOS / UEFI Basics

Before booting from a USB drive to install Ubuntu, you need to understand your computer’s firmware type and how to enter the settings interface. This page will help you master these fundamentals.

BIOS vs UEFI

Legacy BIOS

BIOS (Basic Input/Output System) is the firmware standard used by older computers:

• Uses the MBR (Master Boot Record) partition table
• Supports a maximum disk size of 2 TB
• Basic interface, usually keyboard-only
• Slower boot times
• Commonly found on computers manufactured before 2012

UEFI

UEFI (Unified Extensible Firmware Interface) is the modern firmware standard:

• Uses the GPT (GUID Partition Table) partition table
• Supports very large disks (well beyond 2 TB)
• Graphical interface with mouse support
• Faster boot times
• Supports Secure Boot
• Standard on computers manufactured after 2012

How to check: If your computer was purchased after 2015, it almost certainly uses UEFI. In an existing Windows installation, press Win + R, type msinfo32, and check the “BIOS Mode” field.

Secure Boot

Secure Boot is a UEFI security feature that verifies whether software loaded during the boot process has been digitally signed.

Ubuntu and Secure Boot

Ubuntu fully supports Secure Boot. Ubuntu’s boot loader (shim and GRUB) has been signed with Microsoft’s certificate, so it can be installed and booted normally with Secure Boot enabled.

In most cases, you do not need to disable Secure Boot to install Ubuntu 26.04.

When You Might Need to Disable Secure Boot

The following scenarios may require temporarily disabling Secure Boot:

• Installing certain third-party proprietary drivers (e.g., NVIDIA proprietary drivers)
• Using unsigned kernel modules
• Compatibility issues with some older hardware

How to Enter BIOS / UEFI Settings

You need to press a specific key during boot to enter the firmware settings interface. The key varies by brand:

Common Brand Key Mappings

Tip: You need to start pressing the key repeatedly as soon as you see the brand logo. If you miss the window, restart and try again.

Entering UEFI Settings from Windows

If the key-press method doesn’t work, you can enter from within Windows:

1. Open Settings -> System -> Recovery
2. Under “Advanced startup,” click Restart now
3. After restarting, select Troubleshoot -> Advanced options -> UEFI Firmware Settings
4. Click Restart to enter the UEFI settings interface

Key Options in UEFI Settings

After entering UEFI settings, the following options are relevant to Ubuntu installation:

Boot Order

Controls which device the computer boots from first. When installing Ubuntu, you need to set the USB drive as the first boot device, or use the boot menu to temporarily select it.

Secure Boot

As mentioned above, Ubuntu supports Secure Boot. If you encounter issues, you can temporarily disable it here.

CSM (Compatibility Support Module)

CSM provides legacy BIOS boot compatibility in UEFI mode. It is recommended to disable CSM and use pure UEFI mode for installing Ubuntu, which provides better compatibility and faster boot times.

Fast Boot

Some motherboards’ fast boot feature may skip USB device detection. If the USB drive is not recognized, try disabling Fast Boot.

With this foundational knowledge, you can proceed to the next step: booting from the USB drive.