Does anyone know the difference between adderall and adderall XR?

I have been on adderall for about 6 months now. I have been diagnosed with ADHD about 7 years ago. I take 40 mg of reg adderall and I take my last dose around 6 and then I start feeling sleepy. I also take ambion for my insomia. How long does Adderall XR last and is it better than regular Adderall?