title: Packing and unpacking data for SSE/SSE2 instructions?
body: <p>I'm trying to learn more about how SSE/SSE2 work: I know that SSE/SSE2 use mmx registers with a size of 128 bit (16 byte) and that usually these registers have 4 float cells where I can store my floats by packing. Before getting the result I should "unpack them".</p>
  
  <p>My question is: since I'm a noob, why should I pack these values into xmm registers and why should I unpack them? What's the advantage in this?</p>