Compatibility with Microsoft Corp.'s Windows is crucial to the success of Apple's iTunes Music Store and Apple's goal of selling 100 million songs online by April 28, the first anniversary of the service, Jobs said. Since April, Apple has sold 13 million songs.

The move also should boost sales of Apple's iPod music players, the only portable digital devices that works with the iTunes store.

Since the splashy debut of the Mac version in April, Apple has taken a leading position in the markets for portable digital players and downloadable songs.

"And that's without Windows," said Jobs, demonstrating the service at the Moscone Center in downtown San Francisco.

But Apple's Macintosh operating system is used on only about 2 percent of the world's PCs, whereas the vast majority, more than 90 percent, use Windows.

"They have to disconnect from Macintosh and become more broad-based," said Gartner Inc. analyst Martin Reynolds.

The strategy also is meant to attract more consumers to Apple hardware, said John Buckingham, with Al Frank Asset Management in Laguna Beach.

"It's geared to selling more iPods," said Buckingham, who helps manage $275 million in assets, including 60,000 Apple shares. "It's like the old Schick/Gillette strategy — give customers the razor, but sell them the blades. This is the opposite: Give customers the blades, and sell them the razor."

By early next year, as many as a dozen companies are expected to offer online music stores, including Dell, Amazon.com and Yahoo.

All of the services must compete with numerous sources of free but unauthorized copies of songs.

Songs downloaded from the Windows-compatible version of Apple's Music Store for 99 cents each can be copied to compact discs a virtually unlimited number of times. They also can be transferred to iPods or copied onto three computers simultaneously — the same flexibility Apple offers for Mac users.

Jobs confirmed a report that Apple would team up with PepsiCo Inc. in a promotion to give away 100 million songs next year.

Apple also will partner with America Online, the nation's largest Internet service provider, by adding an "iTunes" button next to songs on AOL's own music service.