a sorting apparatus is composed of sort processors connected in a pipeline fashion . each sort processor 106 merge sorts data from the preceding sort processor and then outputs the merge sort result to the succeeding sort processor . the sort processor includes sort core portions and a front end internal storage and a back end internal storage for the respective sort core portions . outside the sort processors , there are added external memories for the respective sort core portions . the front and back end internal storages and the external memories constitute a local memory . the sort core portions use , when a faulty area is found in the local memory , part of the front end and back end internal storages as an alternative memory .