This is tangental, but I find this an interesting topic - your memory not limited, at least not the way most people think it is. To be accurate - a body of experiments has failed to turn any evidence for old knowledge preventing formation of new knowledge, or new knowledge pushing out the old.
What prevents formation of new knowledge is time - you could learn A or B, but not both at the same time. What makes us forget piece A is not the piece B committed after A, but absence of repetition of A. If you repeat A every so often, you will remember it equally well regardless of whether you also repeat B or not during the same period.
I get my information from this book, which in turn has references to all of the underling studies: http://www.amazon.com/The-Shallows-Internet-Doing-Brains/dp/...