While design modifications could help Apple distinguish its devices from rival phones and tablets, they risk alienating longtime users.
Raluca Budiu, a senior researcher specializing in usability at the Nielsen Norman Group, said the so-called "flat" design can confuse users because it can offer fewer signals about where to tap or click. That's been the case, she said, with Windows 8, which has a very "flat" design. Budiu said it's too early to say if it will be an issue with iOS.
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.
Microsoft's radical makeover of the Windows operating system in October 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 on traditional desktops and laptops. Research firm IDC blamed Windows 8 for accelerating a decline in PC sales.
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.
Apple took a jab at its rival, Samsung Electronics Co., which had been touting its Galaxy phones as better than iPhones because they sport near-field communication chips that allow people to share files by bumping phones together.