What for are these connectors on (older) Arduinos?
On Arduino Duemilanove and some other boards (but not on Arduino Uno) there are four small plates near usb socket, numbered 4 3 2 1. On official photos they are just plates, but on my Hong Kong board there are male header pins instead. They are not mentioned in general texts about the board and I can't seem to know the right phrase to successfulli google it.
What are these four connections for?