September 18, 2013, 5:00 a.m.
SAN FRANCISCO — While Apple's new iPhones have hogged the spotlight in recent days, a seemingly more mundane software update may be far more crucial to the tech giant.
On Wednesday, Apple will make available for free a radically redesigned iOS 7 mobile operating system that Apple Chief Executive Tim Cook described as the biggest change to the iPhone since the device's introduction in 2007.
Indeed, some analysts say the iOS 7 represents a bigger departure for users and developers in terms of the experience than the new iPhone 5s and iPhone 5c that go on sale Friday.
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The question now is whether iOS 7 will reinvigorate the gadget that launched the smartphone revolution — but has seen growth slow this year — or will frustrate users and developers as they try to learn the software's interface.
"I think people aren't anticipating how big of a deal the new iOS 7 will be," said Carl Howe, a Yankee Group analyst. "The software is very different than where they've been. And the thing that is going to blow people's mind is that it's going to make it feel like they're getting a new phone."
For that reason, some analysts have even speculated that iOS 7 could damp new iPhone sales this weekend. Will people put off an iPhone purchase because the software makes it feel like they just got a new phone for free?
Analysts will be watching closely for reactions. Some time on Wednesday, iOS 7 will be available as a free download for most Apple mobile devices: the iPhone 4 or later; the iPad 2or later; the iPad Mini; and the 5th generation iPod Touch.
The iOS 7 software arrives almost a year after Cook announced a management overhaul that saw Scott Forstall, who had been in charge of iOS for years, pushed out.
The development of iOS 7 was overseen by his replacement, Craig Federighi, Apple's senior vice president of software engineering. The interface of the new software was created by a team led by Jonathan Ive, Apple's senior vice president of design, who saw his role expand last year to include software as well as hardware designs.
"We're going to witness an event almost unprecedented in our history when overnight virtually hundreds of millions of people download iOS 7 and begin a fantastic new experience with their new devices," Federighi said last week during Apple's iPhone press event.
The new iOS ditches some familiar elements, such as designs meant to mimic real-world equivalents like bookshelves with wood grain. These types of tricks were intended to create a feeling of familiarity when Apple was introducing a revolutionary new device.
But now that smartphones are commonplace, Apple is introducing a new interface with what is being called a more modern look and feel.
On iOS 7, the home screen has a more three-dimensional look, with the apps appearing to float far above the background wallpaper image. The apps have what is described as a "flatter look," losing some of the fake lighting effects that made them appear to be rounded.
Apple has also added new swipe gestures to allow quicker access to control settings. There is a translucent look that lets a user see through different apps that might be running simultaneously. Apps will automatically update as new versions become available. And iOS 7 also includes iTunes Radio, Apple's new streaming music service.
If all goes well, Apple projects that iOS 7 will be used by more people than any single version of the rival Google Android operating system.
"Since we make updates easy, and make them available to as many customers as possible, iOS 7 will quickly become the world's most popular mobile operating system," Cook said at the unveiling of the new iPhones last week.
Still, this has created a big challenge for developers who have been scrambling in recent months to rework their apps for iOS 7.