UEFI
Unified Extensible Firmware Interface (UEFI) is a modern firmware interface that replaces the traditional BIOS. It provides a more flexible and powerful environment for booting operating systems and managing hardware.
UEFI Logo. Public Domain
Firmware bitness
UEFI firmware can be either 32-bit or 64-bit. The bitness of the firmware determines the maximum amount of memory that can be addressed and the types of operating systems that can be booted.
Checking firmware bitness
From Linux
cat /sys/firmware/efi/fw_platform_size
From macOS
ioreg -l -p IODeviceTree | grep firmware-abi
UEFI variables
You can use efivar to get a list of UEFI variables, which are used to store configuration settings and other data that the firmware uses during the boot process.
efivar --list