When your computer says "100 mbps", that means your connection can handle UP TO 100 megabits per second, assuming your connection is actually higher than 100 megabits per second, which if it were, it would be outrageously expensive.
As for your stuffty internet connection, if you live in Philadelphia I'm pretty sure you might have better options. I'm currently with Verizon FiOS but they tend to cost a bit.
BTW, the graph is in percentage.