Digital media already have altered the landscape of the music and movie industries radically.

Will books now be liberated from the printed page on a mass scale? Or as a blogger put it: Have books hit their iPod moment?

Amazon is set to begin shipping its Kindle 2 to customers Tuesday. To recognize the magnitude of the event, mega-selling author Stephen King wrote an original novella, "UR," exclusively for the device.

Prolific best-selling author Danielle Steel joined in last week when she announced that 71 of her books will be offered digitally. This news followed similar moves by John Grisham and Tom Clancy, who also are jumping on the e-book phenomenon.

While still a small piece of the more than $25 billion American book industry, digital books appear to be growing quickly in popularity. And so are all the options for downloading and retrieval.

Electronic books, or e-books, are digital versions of conventional books that can be downloaded and read on a desktop computer or portable device as small as an iPod.

The Sony Reader Digital Book and Amazon Kindle are the dominant e-book readers in the market.

People who wanted to buy Kindle last year had to get on a waiting list.

"We did not expect the huge demand in the fourth quarter after Oprah [Winfrey] featured Kindle on her show" last October, said Amazon spokesperson Cinthia Portugal.

Amazon credits Kindle with jump-starting its e-book sales. "We have been selling e-books for years, but it didn't work -- until 14 months ago" when the Kindle was introduced, said Amazon.com founder and chief executive officer Jeff Bezos at the launch of the revamped Kindle earlier this month.

"Today, more than 10 percent of the [book] units we sell are Kindle books."

Its newest version, Kindle 2, costs $359.

Amazon offers more than 230,000 titles for Kindle, along with newspaper and magazine subscriptions at a fraction of the cost of a hard copy. Many best sellers and new releases go for $9.99 or less -- although some prices are much higher. There are also many free downloads. Buyers can preview a free chapter or short excerpt before buying.

At a little more than 10 ounces, the Kindle is lighter and around the same size as a typical paperback book. The 6-inch diagonal screen uses an electronic paper display designed to simulate what a printed page would look like, and lighted to eliminate eyestrain.

A button on the device turns pages forward or back. Readers can change the text size, with a choice of six sizes. Kindle automatically saves your place, and you can mark passages or look up words in the built-in dictionary.

The device doesn't need to connect to a computer. Books download directly from Amazon through a wireless connection.

The new version has several enhancements: It's thinner than the original, has a longer battery life and increased storage capacity for 1,500 volumes; the original held around 300. It includes a text-to-speech option that turns it into an audio book player that can read any book file aloud.

The future of the latter is in question. The Authors Guild has challenged the read-aloud feature, charging that it will draw revenues away from audio book sales.

Sony has been a pioneer in the e-book reader field. In October, Sony launched a new model -- the Sony Portable Reader System 700BC ($399.99). Like Kindle, it's also about size of a paperback book, with a 6-inch touch screen and easy-on-the eyes display.

Books purchased through Sony's eBook Store can be read on PCs or Sony readers.

In December, Sony said it had sold 300,000 digital readers since they launched in 2006. Amazon hasn't released any figures for Kindle other than saying it sold out of the first model.

Citigroup analyst Mark Mahaney estimated Kindle sales of 500,000 for 2008. He predicts that Kindle, which he calls "the iPod of the book world," will be a $1.2 billion business by 2010.

But although Sony and Kindle sales picked up before Christmas, there's "still no 'iPod moment,'" Robert Andrews noted in a blog that was picked up on several tech sites. "It's still way short of the 1.3 million units the music player sold in its first two years."

While e-book prices are less than conventional hardbacks and paperbacks, getting started will still set you back by several hundred dollars. But there are less costly alternatives.

A free program for iPhone or iPod Touch called Stanza lets readers download books to a desktop computer or to the iPhone/iPod.

The Stanza reader has many of the same appealing bells and whistles as Kindle and Sony, such as changing type sizes.

Online e-book sellers have entered the market in a variety of ways.

eReader sells downloads for a number of devices, including Windows and Mac systems and many mobile devices. It's currently offering nine free titles from Random House to introduce readers to its collection.

Feedbooks is a site where readers can download e-books to many devices -- Kindle, Sony, iPhone/iPod, smart phones and PDAs.

Audible is an audio book download site, with more than 50,000 titles that can be downloaded to a computer or portable listening device.

Daily Lit is a site where users can download books one chapter at a time via either e-mail or RSS feed. Other online book sellers have found convenient ways to get printed books into readers' hands.

Bookswim is a rental service that works like mail-order movie rentals do on Netflix. For a monthly fee ($19.98 a month for three books to $39.94 a month for 11 books, etc.), subscribers can get books delivered to their mailbox postage-free. If they want to keep a book, they can buy it.

There are several online book swapping sites. At Bookins, for example, members can post unwanted books and DVDs and choose others in exchange.

E-books have their advantages. In crowded urban living spaces, shelves loaded with books aren't an option. The e-book lets people hold on to a large virtual library, or delete books once they've read them.

Some consumers view e-books as environmentally sound, because electronic publishing doesn't consume trees or fuel.

E-books can be a boon to the publishing industry.

"They never go out of stock. There's a faster time to market," Amazon's Ms. Portugal said.

And in a tight economy with shrinking disposable income, the idea of buying a best seller for less than half of its list price is appealing to hardcore readers.

But Eric Ginsberg, vice president of marketing for Bookswim, doesn't see the Kindle/Sony model as a real cost saver.

"It's going to take you 24 books before you even break even. As far as it being a cheap way to read, that I don't buy yet. "

Another drawback: like the iPod, the pricey electronic device makes people easy targets for street crime. It's unlikely that anyone is going to swipe your paperback book on the bus.

Despite all the hoopla over the Kindle, Mr. Ginsberg thinks the e-book phenomenon is still waiting to happen.

"Eventually e-book readers are going to get to the point where music and movies are, where people are accepting of having it on electronic devices. But like music and movies, there was a lot of hype before it actually hit the mainstream."