An electronic book is a book-length publication in digital form, consisting of text, images, or both, and produced on, published through, and readable on computers or other electronic devices. Sometimes the equivalent of a conventional printed book, e-books can also be born digital. The Oxford Dictionary of English defines the e-book as "an electronic version of a printed book," but e-books can and do exist without any printed equivalent. Commercially produced and sold E-books are usually intended to be read on dedicated e-book readers. However, almost any sophisticated electronic device that features a controllable viewing screen, including computers, many mobile phones, and nearly all smartphones, can also be used to read e-books. Some companies, such as Amazon, with their Kindle for PC software, provide an emulator that allows a user to read their format on other platforms.