Driver / Controller

I'm sorry but I'm still not "getting" one thing and I hope someone
can help.

The difference between a DRIVER and a CONTROLLER.

For example, if one of you experienced people were to buy something
like this cool looking thing:

http://cgi.ebay.com/ws/eBayISAPI.dll?
ViewItem&category=25286&item=1923982111&rd=1

You'd notice that it clearly states: "Pack Driver - Stepping Motor
Driver"

Would you then expect to hook a controller up to this? Or would you
expect to make a cable from your PC right to the Pack Driver unit?

PC -> Controller -> Driver -> Stepper

or

PC -> Driver -> Stepper

I don't know why I can't get my head around this, is sounds fairly
straightforward.

Also, would the Xylotex units be considered a controller and a driver
in one?

Thanks
David