After two years of development and beta testing, America Online today quietly premiered the highly anticipated new version of its software, AOL 4.0.

The unveiling comes seven months after the online giant rolled out a "limited preview" of the software.

For the current release, AOL users will be able to download the new software either by clicking a button on the proprietary service's welcome page or by typing keyword "upgrade." A download link will be posted on AOL.com within the next few days, the company said.

The process of developing the software took two years. But David Gang, senior vice president of strategic development at AOL, said the company took longer in order to get a higher-quality product.

Most members have been using AOL 4.0--albeit in beta form--for months. The rollout of the final version, however, means AOL has given the product its final stamp of approval.

The 4.0 software includes a redesigned interface, with such features as more graphics-based icons along the toolbar and a sidebar in channel pages that links to other channels for faster surfing. AOL 4.0 also comes with additional bells and whistles such as spelling and grammar checks on its email client, an address book that can be alphabetized, and the ability to switch screen names without signing off.

Gang declined to comment on how many downloads the software has received since it posted the button for the final product on its Web page. Historically, its initial software releases have been large. For example, when AOL 4.0's public beta was released, 50,000 users downloaded it in less than 24 hours.

The software is currently available only for Windows-based platforms. A Macintosh preview version was released recently, but the company declined to say when a final version of AOL 4.0 for Mac would be released--only that "it will be closer upon the heels of the Windows release than ever before," said a company spokeswoman.

This fall, AOL will ramp up its marketing campaign to attract new users and to upgrade existing ones by means of mass distribution of its CD-ROMs.