One variation of the merge sort method is to modify the splitting operation as follows:
Copy some fixed number of elements into main memory, sort them using an internal sorting method such as quicksort, and write this sorted list to FI; then read the same number of elements from F into main memory, sort them internally, and write this sorted list to F2; and so on, alternating between F1 and F2.
Write a function for this modified merge sort scheme, using quicksort to sort internally the subsists containing SIZE elements for some constant SIZE.