Editing External sorting (section)

== Model ==
{{See also|External memory model}}
External sorting algorithms can be analyzed in the [[external memory model]]. In this model, a [[Cache (computing)|cache]] or internal memory of size {{mvar|M}} and an unbounded external memory are divided into [[Blocking (data storage)|blocks]] of size {{mvar|B}}, and the [[running time]] of an algorithm is determined by the number of memory transfers between internal and external memory. Like their [[cache-oblivious algorithm|cache-oblivious]] counterparts, [[asymptotically optimal]] external sorting algorithms achieve a [[running time]] (in [[Big O notation]]) of <math>O \left(\tfrac{N}{B}\log_{\tfrac{M}{B}} \tfrac{N}{B} \right)</math>.