With physical books, figuring out where pages should start and end is easy: the stream of text is simply divided by how much of it can fit on a page. On a screen, however, users can modify how much text fits by zooming, switching to a different device, or switching reading mode. The only logical option was to hijack virtual page division points from existing print editions.
"Adding 'real' page numbers means we had to find a way to match specific text in a Kindle book to the corresponding text in a print book and identify the correct page number to display," reads an article by Kindle editors that was posted Wednesday on Amazon's blog.
In order to pull off its real pages, Kindle developed algorithms to match the text of print books to Kindle books. (As a top seller of print books, Amazon apparently already had a lot of data about them available.) It stores all of these page-matching files on the web. The team "even found a way to deliver page numbers to books that customers had already purchased."