I think is bytes.. not sure..
But if you ask an ISP on why you dont down load they will tell you this:
"We garentee upto 750kb speed" the the actual 750k
Why arent you getting the speed.. A few factors.. The age of teh phone line in your house, how many splitters in your home. And most importantly, How long of a copper line are you on till you hit the switch that converts to fiber optic.