The difference is that the PCMCIA card doesn't extrude from the laptop. That thing is awesome, never seen one.

I've only seen those that have either a large RJ45 connector extruding from the card, like: http://www.automation-drive.com/EX/05-13-21/a88fa.jpg

Or where you'd needed an adapter dongle that connected to the PCMCIA card.

I know there was a laptop or at least a concept of it with something similar to the (parent) XJACK connector, but have never seen it in real life. Would love to see them in ultrabooks.