Intel® Fortran Compiler 16.0 User and Reference Guide
The Fortran language standard specifies little about the storage of data types.
This loose specification of storage for data types results from a great diversity of computing hardware. This diversity poses problems in representing data and especially in transporting stored data among a multitude of systems. The size (as measured by the number of bits) of a storage unit (a word, usually several bytes) varies from machine to machine. In addition, the ordering of bits within bytes and bytes within words varies from one machine to another. Furthermore, binary representations of negative integers and floating-point representations of real and complex numbers take several different forms.
The simplest and most reliable means of transferring data between dissimilar systems is in character and not binary form. Simple programming practices ensure that your data as well as your program is portable.