trees and external storage internal memory (of courseall these sizes would be much larger in real situation figure shows the file before sortingthe number in each record is its key value ablock sort block sort block sort merge file sort file merge block file file merge figure mergesort on an external file internal sort of blocks in the first phase all the blocks in the file are sorted internally this is done by reading the block into memory and sorting it with any appropriate internal sorting algorithmsuch as quicksort (or for smaller numbers of records shellsort or insertion sortthe result of sorting the blocks internally is shown in figure second file may be used to hold the sorted blocksand we assume that availability of external storage is not problem it' often desirable to avoid modifying the original file merging in the second phase we want to merge the sorted blocks in the first pass we merge every pair of blocks into sorted two-block sequence thusthe two blocks -