When to use the 'ieee-le.l64' machine format in FOPEN?

fopen can use the machine formats (see "help fopen"):

 'ieee-le'     or 'l' - IEEE floating point with little-endian
                        byte ordering
 'ieee-le.l64' or 'a' - IEEE floating point with little-endian
                        byte ordering and 64 bit long data type

What is the difference between these formats? 64 bit integers can be read in the 'l' format without problems.

Does the machine format a file is opened in concern the 'long' and 'ulong' precision of fread only and nothing else? See "help fopen":

 'long'    integer,  32 or 64 bits.
 'ulong'   unsigned integer,  32 bits or 64 bits.

Bump.

Final bump. What do you suggest: Should I delete the thread when I do not find a (useful) answer?