Newton books provide all the functionality of ordinary books but add searching and hypertext capabilities. The format was invented for the Newton to provide a means of making volumes of data portable, and is particularly popular in the medical community as most medical references are available as Newton books and carrying around a one pound Newton is preferable to carrying around twenty pounds of books, especially when it comes to looking up something. In addition to medical books, numerous references, most of the classics, and many contemporary works of fiction are available as Newton books. Most fiction is available for free, most references cost money. Newton books are somewhat more capable than the similar Palm DOC; both are specific types of e-books.