A couple of years ago, before SSE existed, I wrote a highly optimized memory copy routine. It was more than just using movntq (non temporal is important to avoid cache pollution) and the like, for large data I copied the chunks in a local buffer less than one page size and copied it to the destination. Sounds crazy? It actually was much faster because of page locality.

For small chunks however, nothing was faster than rep movsb which moves one byte at the time.