First of all what is a vector Array data structure http://en.wikipedia.org/wiki/Array_data_structure
now you get it you can fill a big vector array data structure with small vector array data structures.
for the CPU it doesn't matter he can calculate it as 1 single vector array.
because SIMD means calculating all data in the same time in a loop-level parallelism.
this calculating of many small vector arrays is also called Parallel array http://en.wikipedia.org/wiki/Parallel_array
maybe now you get it. its the same with x86 cpus they also calculate 2 SSE instructions in a 128bit vector unit and 4 in a 256bit vector unit.