Variations of Merge Sort
Oscillating merge sort: Oscillating merge sort/oscillating sort is a variation of MG (merge sort) used with tape drives that can read backward. Instead of doing a complete distribution as is done in a tape merge, the distribution of the input and the merging of runs are interspersed. It does not waste rewind time or have tape drives sit idle as in the conventional tape merge.

Cascade Merge Sort: It is similar to the polyphase merge sort but uses a simpler distribution. The merge is slower than a polyphase merge when there are fewer than six files, but faster when there are more than six.

Polyphase merge sort: It is an algorithm which decreases the number of runs at every iteration of the main loop by merging runs into larger runs. It is used for external sorting.