A SIMD processor responds to a single min/max instruction to find the minimum or maximum valued data unit in an array of data units. The determined minimum/maximum value and an associated index value thereto may be output. Alternatively, the value of a data unit in another array may be output at a corresponding location. A further single instruction executable by the SIMD processor, may be applied to results obtained using such a single min/max instruction, to allow such instructions to operate on two dimensional arrays.