An e-reader, also called an e-book reader or e-book device, is a mobile electronic device that is designed primarily for the purpose of reading digital e-books and periodicals. Any device that can display text on a screen may act as an e-reader; however, specialized e-reader devices may optimize portability, readability, and battery life for this purpose. Their main advantage over printed books is portability. This is because an e-reader is capable of holding thousands of books while weighing less than one book, and the convenience provided due to add-on features. Overview An e-reader is a device designed as a convenient way to read e-books. It is similar in form factor to a tablet computer, but often features electronic paper rather than an LCD screen. This yields much longer battery life — the battery can last for several weeks — and better readability, similar to that of paper even in sunlight. Drawbacks of this kind of display include a slow refresh rate and (usually) a grayscale-only display, which makes it unsuitable for sophisticated interactive applications as those found on tablets. The absence of such apps may be perceived as an advantage, as the user may more easily focus on reading. The Sony Librie, released in 2004 and the precursor to the Sony Reader, was the first e-reader to use electronic paper. Many e-readers can use the internet through Wi-Fi and the built-in software can provide a link to a digital Open Publication Distribution System (OPDS) library or an e-book retailer, allowing the user to buy, borrow, and receive digital e-books. An e-reader may also download e-books from a computer or read them from a memory card. However, the use of memory cards is decreasing as most of the 2010s era e-readers lack a card slot. History An idea similar to that of an e-reader is described in a 1930 manifesto written by Bob Brown titled The Readies, which describes "a simple reading machine which I can carry or move around, attach to any old electric light plug and read hundred-thousand-word novels in 10 minutes". His hypothetical machine would use a microfilm-style ribbon of miniaturized text which could be scrolled past a magnifying glass, and would allow the reader to adjust the type size. He envisioned that eventually words could be "recorded directly on the palpitating ether". The establishment of the E Ink Corporation in 1997 led to the development of electronic