" The measuring rod, the unit of information, is something called a bit (for binary digit). It is an answer - either yes or no- to an unambiguous question...
The information content of the human brain expressed in bits is probably comparable to the total number of connections among the neurons- about a hundred trillion, 10^14 bits. If written out in English, say, that information would fill some twenty million volumes, as many as in the world's largest libraries. The equivalent of twenty million books is inside the heads of every one of us...
When our genes could not store all the information necessary for survival, we slowly invented them. But then the time came, perhaps ten thousand years ago, when we needed to stockpile enormous quantities of information outside our bodies. We are the only species on the planet, so far as we know, to have invented a communal memory stored neither in our genes nor in our brains. The warehouse of that memory is called the library...
The great libraries of the world contain millions of volumes, the equivalent of about 10^14 bits of information in words, and perhaps 10^15 bits in pictures. This is ten thousand times more than in our brains. If I finish a book a week, I will only read a few thousand books in my lifetime, about a tenth of a percent of the contents of the greatest libraries of our time. The trick is to know which books to read...
Books permit us to voyage through time, to tap the wisdom of our ancestors. The library connects us with the insights and knowledge, painfully extracted from Nature, of the greatest minds that ever were, with the best teachers, drawn from the entire planet and from all of our history, to instruct us without tiring, and to inspire us to make our own contribution to the collective knowledge of the human species. Public libraries depend on voluntary contributions. I think the health of our civilization, the depth of our awareness about the underpinnings of our culture and our concern for the future can all be tested by how well we support our libraries. p224-233 "

― Carl Sagan , Cosmos