http://home.howstuffworks.com/sewing-machine1.htm
Beautiful diagrams explaining it all.
Actually, I hadn’t really heard of the bobbin-less “chain stitch.” I can see why it was invented first.
However, I could never understand how the top thread with a bobbin worked — now I see the upper thread wraps all the way around the bobbin assembly, looping the top around.
Obviously, there is a lot of thread twisting going on, and I still don’t really see how the top thread goes around the bobbin when it is mounted in on a pin, but at least I get the concept!