History of File Structures IV. Balanced Trees
In 1963, researchers came up with the idea of AVL trees for data in memory.
AVL trees, however, did not apply to files because they work well when tree nodes are composed of single records rather than dozens or hundreds of them.
In the 1970’s came the idea of B-Trees which require an O(logk N) access time where N is the number of entries in the file and k, th number of entries indexed in a single block of the B-Tree structure --> B-Trees can guarantee that one can find one file entry among millions of others with only 3 or 4 trips to the disk.