Comment by Bilirubino

The situation is that OCaml is giving you all the options:

(a) int has 31 bits in 32-bit architectures and 63 in 64-bit architectures (which speed up some operations)

(b) the standard library also provides Int32 and Int64 modules, which support platform-independent operations on 32- and 64-bit signed integers.

In other words: int is different but you always have standard Int32 and Int64 in case you need them.

It seems therefore that the use for system-level programming should not be decided for this (although the fact that it is a garbage collected language can be important depending on the case, note that still its garbage collector has been proved one of the fastest in the comparisons and evaluations done by the Koka language team of developers).