SAN FRANCISCO —Apple kicked off its worldwide developers conference Monday by talking about the newest versions of its desktop and mobile operating systems, OS X Yosemite and iOS 8.

Monday's keynote began with a video celebrating developers and the mobile applications they build for Apple's devices. Apple CEO Tim Cook then arrived on stage and maintained that theme, thanking developers for their work to expand and improve the Apple ecosystem.

"We now have 9 million registered developers," Cook noted, explaining that the total increased 50 percent in the past year, the largest developer growth in Apple history.

Cook said that the newest version of Apple's desktop software, OS Mavericks, is now running on more than half of Mac desktops less than a year after its introduction; Cook compared that with Windows 8, which he said is running on just 14 percent of Microsoft computers. Cook returned to that theme later, showing that 89 percent of Apple mobile devices were using the latest iOS, while only 9 percent of Android users have the newest version of Google's mobile operating system.

Apple software executive Craig Federighi took the stage first to show off the coming version of OS X, which will be called Yosemite.

Bundled with Yosemite will be an update to iCloud called iCloud Drive, which allows users to see their saved files in folders on Apple and Microsoft devices, and new e-mail features including the ability to send larger files and manipulate photos and documents such as PDFs. Apple also featured a revamped Safari Web browser that Federighi promised would be more power-efficient and faster than rivals Firefox or Chrome.