As far as knowing which books I have read on my Kindle and Kindle Paper white, when I open my "library" or list of books, each one shows the percentage of the book that has been read so I can tell immediately the ones I've already read and the ones that I've started but didn't like. They might say 20% or so if I didn't like them. I could go in and delete them but I seldom take the time to do that. Another feature that enjoy is that if I try to buy or download a book I already have, my Amazon account tells me. I do tend to forget the names of books I've read. Whether I'm getting ebooks from the library, cheap books from Bookbub or buying from Amazon, it all goes through my Amazon account which is very convenient for me.