As an estimate of the size of the Gutenberg Galaxy, as of 2002/2003, the British Library claimed that it held over 150 million items, and the Library of Congress claimed that it held approximately 119 million items.
Given an estimated average book size of 6 Mbytes for a purely textual book containing 1 million words, this represents roughly 1,000,000,000,000,000 bytes (1015 bytes) of text.