1. A method for using a memory array, the method comprising: (a) providing a memory array comprising a plurality of memory cells, each memory cell comprising a memory element comprising a switchable resistance material configurable to one of at least three resistivity states; (b) in a first set of memory cells, using X resistivity states to represent X respective data states; and (c) in a second set of memory cells, using Y resistivity states to represent Y respective data states wherein X≠Y.