Understanding the "BIOS Legacy Boot of UEFI Only Media" Error When Booting from a USB Drive

Encountering the "BIOS Legacy Boot of UEFI Only Media" message while trying to boot from a USB drive usually means there’s a mismatch between the BIOS boot mode and the type of media you're attempting to boot from.

What Are Legacy Boot and UEFI?

There are two primary boot modes: Legacy and UEFI. Legacy Boot is an older boot method supported by BIOS, while UEFI (Unified Extensible Firmware Interface) is a more modern approach that enhances compatibility with current operating systems and hardware.

• Legacy Boot: typically used on older systems, with limited functionality, supporting filesystems like FAT32.
• UEFI Boot: designed for newer systems, supporting larger disks and more advanced security features, such as Secure Boot.

Causes of the "BIOS Legacy Boot of UEFI Only Media" Error

The "BIOS Legacy Boot of UEFI Only Media" message means that your BIOS is set to boot in Legacy mode, but the USB drive is formatted in UEFI mode. The BIOS can't locate a compatible boot sector on the device because UEFI media doesn’t support Legacy boot.

How to Resolve the Error

To resolve this error, you have a few options:

1. Change Boot Mode to UEFI in BIOS Settings

Enter your system’s BIOS, locate the boot options, and set the boot mode to UEFI instead of Legacy. Save your changes and restart. This allows the system to recognize UEFI media and boot from it.

2. Recreate the USB Drive in Legacy Mode

If your BIOS doesn’t support UEFI or you prefer to boot in Legacy mode, try recreating a Legacy-compatible bootable USB drive. Use tools like Rufus and select the "MBR" option for older BIOS systems.

3. Enable Compatibility Support Module (CSM)

Some BIOS versions offer a combined boot mode, known as CSM (Compatibility Support Module), which supports both Legacy and UEFI boot. Enable CSM if available to allow flexibility in booting from different types of media.