Apple's iOS 4 was released today ahead of the launch of the iPhone 4, which becomes available June 24. iPhone users can update to the latest OS via iTunes, but some features will not be available for the iPhone 3G and the update is not available at all for the original iPhone. iOS 4 will not be available on the iPad until this fall.

Apple says there are more than 100 new features in iOS 4, but the most notable tweaks include multitasking, with handy controls for switching apps; home screen folders that you can name by category for easy access to similar apps; a unified e-mail in-box so you no longer need to switch among accounts; and many more. Check out our slideshow for iOS 4.

Jason Parker has been at CNET for more than 13 years. He is the Senior Editor in charge iOS software and has become an expert reviewer of the software that runs on each new Apple device. He now spends most of his time covering Apple iOS releases and third-party apps.