SAN FRANCISCO - Apple is throwing out most of the real-world graphical cues from its iPhone and iPad software, like the casino-green "felt" of its Game Center app, in what it calls the biggest update since the iPhone's launch in 2007.
The new operating system, called iOS 7, strives for a clean, simple, translucent impression. Apple is redesigning all its applications and icons to conform to the new look, driven by long-time hardware design guru Jony Ive.
The operating system will show up on most iPhones, iPad and iPod Touches this fall, the company said.
The overhaul represents Ive's attempt to freshen the look of both the iPhone and the iPad in hopes of deepening users' attachment to the trendsetting devices. It comes at a time when rivals such as Samsung Electronics and Google are trying to get people to defect by developing their own lines of elegant and often less-expensive products.
The stiffer competition has slowed Apple's growth in the increasingly important mobile-device market, contributing to a 38 percent decline in the company's stock price since the shares peaked at $705.07 in September.
Wall Street didn't seem nearly as impressed with Apple's new software approach as the sold-out audience of enthusiastic application developers who flocked to San Francisco on Monday. Apple's stock dipped $2.92 to close Monday at $438.89.
The redesigned software uses simple graphical elements in neon and pastel colors. Gone is the effort to make the icons look like three-dimensional, embossed objects - a tactic known as "skeuomorphism" that was favored by Apple's late CEO and co-founder, Steve Jobs.
Interface designers call the new guiding principle "flat," but on the iPhone's main screen, the background image will move subtly with the movement of the device, creating an illusion of depth. Other screens include plenty of white space.
Among other changes, Apple's new iOS system will update apps automatically. It will store Web passwords online in Apple's syncing service, iCloud, making them available across devices. The AirDrop feature will allow sharing of big files with Apple-equipped people in the same room.
While the design modifications could help Apple distinguish its devices from rival phones and tablets, the company risks alienating longtime users.
"The new version is almost unrecognizable, which will make it polarizing," predicted Ovum analyst Jan Dawson. "Some people will love that their phone feels new and different, while others will be disoriented by the newness."
The so-called "flat" design can confuse users, because it can offer fewer signals about where to tap or click, said Raluca Budiu, a senior researcher specializing in usability at the Nielsen Norman Group. That's been the case, she said, with Microsoft's Windows 8, which has a very "flat" design.
What remains to be seen is whether Apple was fixing something that wasn't broken. Budiu noted that iOS users seem quite happy with the current iOS, which is easier to use than Google Inc.'s Android, its only big competitor.
Apple made a rare, major stumble with last year's iOS update, when it replaced Google's Maps application with its own navigation app. The underlying data for Apple's Maps was spottier and less accurate than Google's, users found. The Maps fracas didn't diminish the demand for iPhones, however.
Microsoft's radical makeover of the Windows operating system in October provides a stronger example of the dangers of software revamps. Windows 8 was meant to give the company a stronger presence on tablet computers, but it ended up confusing many people who had become accustomed to using the old operating system.