The number of bits in a file storage 1 unit is given by the constant FILE STORAGE SIZE (13.8.2.9) defined in the intrinsic module ISO FORTRAN ENV. It is recommended that the file storage unit be an 8-bit octet where this choice is practical. NOTE 9.13 The requirement that every data value occupy an integer number of file storage units implies that data items inherently smaller than a file storage unit will require padding. This suggests that the file storage unit be small to avoid wasted space. Ideally, the file storage unit would be chosen such that padding is never required. A file storage unit of one bit would always meet this goal, but would likely be impractical because of the alignment requirements. The prohibition on alignment restrictions prohibits the processor from requiring data alignments larger than the file storage unit. The 8-bit octet is recommended as a good compromise that is small enough to accommodate the requirements of many applications, yet not so small that the data alignment requirements are likely to cause significant performance problems.
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