A "USB low-level format" generally refers to operations that reinitialize a USB mass storage device at a very low layer — wiping partitions, reinitializing the filesystem or FAT structures, and sometimes rewriting device-specific metadata (like vendor-managed firmware areas, allocation tables, or Bad Block Tables on some flash controllers). "501 upgrade code" appears to be a specific firmware or tool-version label; without a vendor context it likely means a firmware revision or a utility command set for a particular USB controller or device family. This post explains concepts, risks, typical methods, and a hypothetical "501 upgrade code" workflow for advanced users and developers.
sync && sudo eject /dev/sdb