Accessing the harddisk is about 1000 times slower than RAM access. And if the calculation of the permutations of more than 52 symbols (from your last post) takes some years, writing this to the disk will exceed the life time of the computer in every case.
The solution is easy: Do not do this. There is simply no reason to calculate a giantic array which such a tiny density of information. It will be more efficient to create the single lines (or rows) dynamically. For permutations this can be done e.,g. by:
