With NOR memory, all memory locations are guaranteed to be good and to have the same level of endurance. To improve yields and keep costs down, NAND flash contains randomly located bad blocks in the array.

Since cost is a function of die size, NAND Flash are lower cost for the same size. Also, for NOR memory, a relatively large amount of extra memory cells are fabricated on the die; these are used to “repair” defects in the memory array in order to produce a device that has “all good” memory locations. But for NAND, a minimal amount of extra memory is set aside to repair defective regions on the die because it is not necessary to repair the entire array. This further reduces the size (and therefore the cost) of a NAND die relative to NOR.