Number of elements that can acted upon, examples

If we vectorize the code, we can perform, with a 128-bit register four simultaneous operations, that is we have

for (i = 0; i < n; i+=4){
    a[i] = b[i] + c[i];
    a[i+1] = b[i+1] + c[i+1];
    a[i+2] = b[i+2] + c[i+2];
    a[i+3] = b[i+3] + c[i+3];
}

Four additions are now done in a single step.