So it is supposed to be very fast to have an array of say 5 million integers stored in a binary file and do a = numarray.fromfile('filename', (2, 2, 2)) numarray.add(a, 9, a) but how is that faster than reading the entire file into memory and then having a for loop in C: (loop over range) { *p++ += 9 } or is that essentially what's going on?