Well, there are now two electronic books on the market, and more are coming. The Rocket eBook, by NuvoMedia, and the SoftBook, by SoftBook Press, both hit the market late last year, with the ability to download electronic versions of books that users could buy online. This spring both added a key new feature: the ability to store and display documents written by individuals and companies, in addition to retail books. People have been trying to use computers as books for years, with generally poor results.

Lots of classics, and afew more recent titles, have been made available on CD-ROM or the Web in electronic form. But PC screens -- never designed for long books -- turn reading into a tedious chore. So there's probably a market for a dedicated electronic book, or at least there will be someday.

The first two entries in the field have taken very different design paths, with very different results. One, the SoftBook, strives to look and feel as much as possible like a traditional book -- it even has a leather cover -- and doesn't require a personal computer. It connects directly to the Internet for buying and downloading books. This is a bold and welcome move because it opens the SoftBook to millions who don't have PCs and cuts out all the balkiness of a PC. But it also has some drawbacks. The other, the Rocket eBook, is unabashed about looking like a little computer. It also is chained to the PC, which it needs to connect to the Internet and to store downloaded books that exceed its internal capacity.

But this more conventionalapproach creates some key advantages. The $499 Rocket has the dimensions of a large paperback and weighs a little over a pound. Both righties and lefties can easily press the two page-turning buttons with a thumb. The screen is small -- about 5.5 inches diagonally -- but it's sharp and was easily readable in all the lighting conditions I tried. The text is plain and doesn't strive to look like a paper book, but you can download various font sizes and typefaces via your PC.

You can view the text either vertically or horizontally and flip it to accommodate left-handers. Icons at the edges of the screen let you highlight words, set bookmarks, add notes and flip through pages. To buy books for the Rocket, you use your PC and a Web browser to reach Barnes & Noble -- a part owner of NuvoMedia -- which operates a special online bookstore for Rocket editions. The selection is small -- about 440 titles at this writing -- and prices, absurdly, are about the same as for paper editions.

After you buy a book, it'sdownloaded in encrypted form to your hard disk and transferred to the Rocket e-Book via a cradle that attaches to the PC and special software called the RocketLibrarian. The Rocket can hold about 10 full books, and its nonremovable battery lasts for 20 hours.

Now you can also add your own documents with the RocketWriter. This function, which works through the RocketLibrarian software, will import to your Rocket any document you save in HTML, the format of Web pages, including graphics. You can also directly download Web sites into your Rocket. In my tests, RocketWriter showed promise, but some documents and Web sites left it flummoxed. And even when it did the job right, graphics weren't properly displayed or laid out. But for simple, text-only documents, it worked fine.

The larger SoftBook is about the size of a piece of paper and weighs around 3 pounds. Its signature feature is a soft leather cover that serves as a power switch. When you open the cover, the SoftBook lights up. The screen is about 9.5inches diagonally and is surrounded by four buttons that control the turning of pages and the summoning of various simple menus. Screen icons are activated by tapping on them with a plastic stylus.

To buy and download books, you just plug a phone line into the built-in modem and you're instantly connected to the SoftBook online store. In my tests, this worked well. The SoftBook's big screen allows books to look much like they do on paper, and there is plenty of room for navigation controls that let you jump around from section to section, set bookmarks, and highlight and annotate passages. But the SoftBook has a number of key weaknesses.

I thought the screen lacked contrast, especially outdoors or in bright light. Standard memory is cramped, and a SoftBook can hold only two or three typical books without a memory upgrade. Others you buy are stored on SoftBook's remote computer, and you must dial in again to get to them. The battery life, just three to five hours, is unacceptable. And the SoftBook isexpensive. Users have to pay $299 up front and commit to spend at least $20 a month for two years at the online bookstore, a total of nearly $800.

An alternative plan offers the product at $599 with no monthly fee. SoftBook is aimed more at corporate users. Its selection of retail titles is more limited than Rocket's, and its new method for uploading documents is tailored to corporate manuals, reports and the like, rather than to individual files. I like the SoftBook and believe it will evolve into a good consumer product, especially since it's unshackled from the PC.

But on balance, I prefer the Rocket eBook, with its lower price, greater storage, easier handling of personal documents, longer battery life and more readable screen. That said, neither of these devices can compete yet with a paper book, which costs much less, never runs out of battery power and is easy to read. And perhaps that's just as well.

(Walt Mossberg's Smart Machines column appears monthly in SmartMoney, The Wall Street JournalMagazine of Personal Business, published by Hearst Communications Inc. and Dow Jones & Company Inc. To learn more, visit SmartMoney.com)