OCaml uses a tag bit to distinguish ints from pointers, so (unboxed) ints are only 31 bits: https://realworldocaml.org/v1/en/html/memory-representation-of-valu

OCaml uses a tag bit to distinguish ints from pointers, so (unboxed) ints are only 31 bits: https://realworldocaml.org/v1/en/html/memory-representation-of-values.html https://realworldocaml.org/v1/en/html/memory-representation-... Floating point numbers are normally boxed (except for float arrays, float-only records, and some cases of local use).