UEFI isn't specific to any processor architecture. It can support modern 32-bit and 64-bit firmware device drivers. The 64-bit capability enables the system to address more than 17.2 billion gigabytes (GB) of memory from the earliest stages of boot.
Note: The 32-bit editions of Windows don't support UEFI features. Only 64-bit editions of Windows can take advantage of the features that 64-bit UEFI firmware enables. Fortunately, the CSM in current UEFI implementations enables 32-bit operating systems and other operating systems that don't support UEFI to boot on hardware that has UEFI firmware. But, operating systems that require a CSM to boot can't use UEFI-specific features because the CSM emulates earlier BIOS.