Info from the source code:

This package provides a user-interface for hex viewing large file!! Hexview mode can open a 5GB file within a second. If you often need view large file for data debugging of probing, Hexview is for you!! For viewing binary content, Hexview mode is much better than the offical hexl-mode(using hexl program piping result in a lot memory waste). The core part of Hexview mode is just a simple builtin function: ‘insert-file-contents-literally’. So Hexview doesn’t need large memory to view large file. Due to the limitation of emacs’s Integer representation , on 32-bit version, you can only view file content up to index ‘268435455’, but in 64-bit version ‘emacs’ the valid range of Integer is much larger. Practically, Hexview mode is enough for 80% of you dailly usage. So enjoy.