When I first became interested in the Arduino and got myself a Uno. I could’ent understand why it never had pins underneath. As the way of working I had come from used stacked boards, these in turn used socket headers which also carried long extended square pins (Great for wire-wrapping)… So if the can plug a shield in to your Uno, etc. Why can’t you plug your Uno in to a shield??
Well that was a few months ago and I am not doing too bad, it’s still the “C” programming that gets me. But I’am on my second Arduino bot, done a capacity meter, etc.
I did also buy a cheap Chinese copy Uno, and a few days ago modified it… by removing the headers and adding sockets with pins. Not a job for the faint hearted, a matter of removing the plastic shell part first, then each individual pin, removing as much solder with a solder sucker first, cleaning and opening up the PTH holes. Then just pop the new sockets in and resolder. Fully tested fully working?
The extended sockets also take any (Especially my home-made shields) way above the USB and power sockets.
The following pictures might make your toes curl!!