The usual answer for such a question about X2 and X1 is that X1 was really slow. It is usually correct, with the proviso that X2 might <i>still</i> be really slow, only less so.<p>With most computer artifacts, it is hard to tell, <i>prima facie</i>, that they are slow, until somebody makes a faster one. Then the original comes to be recognized as slow (although somebody will still insist it's not <i>that</i> slow). The faster one might still be slow, but that fact remains unknown.<p>The fact is that almost everything is slow, in the sense that somebody smarter, more experienced, and more diligent could make it faster, often by doing things that the person who wrote the slow version would have found distasteful.