 It was introduced by Matteo Frigo, Charles Leiserson, Harald Prokop, and Sridhar Ramachandran in 1999 in the context of the cache oblivious model.In the external memory model, the number of memory transfers it needs to perform a sort of formula_1 items on a machine with cache of size formula_2 and cache lines of length formula_3 is formula_4, under the tall cache assumption that formula_5.This number of memory transfers has been shown to be asymptotically optimal for comparison sorts.