More and more people are gazing at electronic-book readers—lightweight slates about the size of a thin paper­back that can store up to 200 downloaded books. Although prior generations fizzled, Sony’s Reader, introduced in 2006, and Amazon’s Kindle, which debuted last year, are both selling well. The key difference is the screen.

Interactive: View the insides of the Kindle E-Reader

Researchers had wrestled with e-book readers for decades, but most sported power-thirsty, backlit LCD screens that glared in low light or were drowned out by bright sunlight. The breakthrough this time is a screen made with “electronic paper” from E Ink Corporation in Cambridge, Mass. Sony, Amazon and other makers worldwide are using the material.

E-paper displays are reflective: ambient light bounces off them, so they look and read like ordinary paper. The screens are very energy efficient, too. “The only power used is when you turn a page,” says Isaac Yang, manager of software product development at Sony in San Jose, Calif. No current is needed to sustain the characters on a page once it has been called up. Yang says about 7,500 pages can be turned on a single battery charge. Downloading books consumes additional power.

Sony’s Reader, roughly $300, has a stated capacity of about 160 books, which are found by linking it to a computer via a USB cable and going to the company’s online bookstore. Amazon’s Kindle, $400, can hold about 200 books and can download them by connecting to Sprint’s wireless data network. Amazon also offers paid subscriptions to certain newspapers and magazines. Newly released books typically cost around $10. Enthusiasts who have posted online reviews note, however, that the software for downloading and managing files can be a bit cumbersome.

The fonts on both the Sony and Amazon handhelds can be made larger or smaller, and both can display black-and-white jpeg and gif images, Microsoft Word documents and RSS news feeds. Each item, of course, will occupy some of the roughly 190 megabytes of memory.

Market analysts remain unsure about whether e-books and readers will ever become ubiquitous. Some people are fiercely attached to the tactility—and even the smell—of paper books and periodicals, whereas others love the idea of carrying around heaps of documents in a device weighing 10 ounces. Perhaps the next frontier—color screens—might sway the masses. E Ink is working on prototype e-paper that incorporates the red, green and blue filters needed to show full-color imagery; such a surface could potentially support downloaded video and books on a screen much bigger than a cell phone but much lighter than a laptop.

Did You Know ...
RESOLVED: Reader screens made with E Ink paper have a resolution of 167 dots per inch (dpi). A typical ink-jet printer achieves 300 dpi, a Web page 72 dpi.

CHINA, FRANCE: eRead Technology’s STAReBOOK is popular in China, as is Bookeen’s Cybook in France. Les Echos, an electronic newspaper publisher in Paris, offers editions that can be downloaded over Wi-Fi connections onto the iLiad reader made by iRex in the Netherlands.

FORERUNNERS: Researchers at Xerox Palo Alto Research Center worked on an oil-filled microcapsule system named Gyricon in the 1970s. In 1971 Michael Hart, a University of Illinois student, obtained mainframe computer time to begin to digitize and archive books and other items, with the goal of someday distributing a massive digital library.

THE LAST BOOK: In 1997 Joseph Jacobson, a young professor at the Massachusetts Institute of Technology’s Media Lab and an eventual founder of E Ink, published a paper called “The Last Book.” In it he envisioned a hardcover book containing several hundred blank electronic pages. Futuristic memory chips in the book’s spine would hold the entire catalogue of the Library of Congress, and a simple control would display any one of those titles on its pages.