Apple on Monday unveiled its hotly anticipated iTunes Radio Service as it announced a dramatic overhaul of the touch-screen interface for its popular smartphones and tablets.

The free Internet radio service features over 200 stations "and an incredible catalog of music from the iTunes Store," Apple said in a statement as it opened its annual developers conference in San Francisco.

The ad-supported free music service is set to launch later this year and "offers music fans access to thousands of new songs every week, as well as serving up exclusive music from new and popular artists before you hear them anywhere else," Apple said.

The service will be integrated with Apple's personal voice-assistant software program Siri, so users will be able to find out "who plays that song?" or ask the program to "play more like this."

"iTunes Radio is an incredible way to listen to personalized radio stations which have been created just for you," said Eddy Cue, Apple's senior vice president of Internet software and services.

"It's the music you love most and the music you're going to love, and you can easily buy it from the iTunes Store with just one click."

Several analysts saw iTunes Radio as a nice feature but lacking the ability to lure people away from popular Internet music rivals.

"The iTunes Radio announcement turns out to be much ado about almost nothing," said Forrester analyst James McQuivey.

"None of what the company announced moves the industry forward or changes the game. Spotify and Pandora have little to worry about from Apple."

The streaming radio service was part of what Apple chief Tim Cook branded the biggest change to iOS -- Apple's mobile operating system -- since the introduction of the iPhone in 2007.

Jonathan Ive, the man behind the winning hardware designs of Apple products, put his mark on the icons, layout and style of the home and lock screens people use to engage with Apple mobile devices.

"There is a profound and enduring beauty in simplicity," Ive said in a video clip played for the approximately 6,000 software developers at the sold-out gathering in downtown San Francisco. "It is about bringing order to complexity."

Changes included transparency and motion-responsiveness that allows users to tilt an iPhone, iPad, or iPod touch to "peek" below icons on screens to see rich images beneath.

The new mobile operating system allows multi-tasking of applications while software behind the scenes works to maximize battery life by more efficiently fetching and managing data.

An Air Drop application sensed when friends with Apple gadgets are near and allowed images, video or other files to be instantly shared, according to senior vice president of software engineering Craig Federighi.

He also showed off improvements to the photo application that included enabling special effects such as those popular at Facebook-owned Instagram.

Another new feature called Activation Lock renders a device inoperable if someone without the owner's Apple ID tries to wipe devices or turn off a gadget-finding feature.

"We think this is going to be a really powerful theft deterrent," Federighi said.

Siri software got an upgrade, including new voice and languages for responses; incorporating Bing internet search, and making the software smarter, according to Cue.

"These enhancements are going to continue to strengthen Apple's leadership in the ecosystem battle for customer loyalty," said Forrester analyst Charles Golvin.

"What customers are getting here is tremendous innovation under the covers: improved lifetime of the product, battery life and experiences that matter to customers -- not whizzy gadgets -- that people will actually use and that will benefit their lives."

Apple has sold more than 600 million mobile devices powered by iOS software, according to Cook.

Apple also unveiled a new-generation Mavericks operating system for its popular Macintosh line of computers and upgraded MacBook Air laptops that boasted ramped up performance at a price $100 less than predecessors.

In a rare deviation from Apple's usual secrecy about products in the works, Apple provided a glimpse at a coming Mac Pro desktop machine for power users such as photographers and film makers.

Radically redesigned Mac Pro hardware shunned the old box-shape, adopting instead the look of a small, black obelisk a fraction of the volume but much more muscular internally.