UEFI vs Legacy BIOS: what it means for booting from USB
BIOS and UEFI are the firmware that starts your computer. Most computers made in the last decade use UEFI. Older ones use legacy BIOS, sometimes called CSM or Legacy mode.
The practical difference
- UEFI supports large disks, faster start-up and Secure Boot. Modern installs use it.
- Legacy BIOS is the older method, still needed by some older computers and systems.
Which entry to pick
In the boot menu a USB drive may appear twice. The entry with UEFI in its name starts in UEFI mode. Pick the UEFI entry on a modern computer. Use the plain entry on older computers.
Keep modes consistent
If Windows was installed in UEFI mode, install Linux in UEFI mode too. Mixing modes can cause boot problems.
See also Secure Boot and Linux and boot menu keys by brand.