It is an obsolete form of docking connector. At one time they offered components like Port Replicators
that would use it.
For my own use I need a laptop that supports full-featured docks and port replicators
, which is another one of the many reasons I use ThinkPads exclusively. When I return to my desk I currently snap my ThinkPad into this dock
, which is connected to multiple external monitors, an eSATA dock, gigabit ethernet, DVD burner, scanner, floppy drive, external speakers, several USB hubs, AC power, etc. I could not imagine having to make all of those connections manually every time I returned to my desk, and several of them would be impossible without the dock. Scott.