These days, most computers use the same internal data formats for integer and floating-point data, if one ignores little differences like big- versus little-endian byte ordering. However, occasionally it is necessary to exchange data between systems with incompatible data formats. This is what portable files are designed to do.
Please note: Although all of the following information is correct, as far as the author has been able to ascertain, it is gleaned from examination of ASCII-formatted portable files only, so some of it may be incorrect in the general case.