iOS 5 is the fifth major version of Apple's iOS, the operating system that runs the iPhone, iPad and iPod Touch. Announced at Apple's Worldwide Developers Conference (WWDC), iOS 5 debuted the following Fall on all supported devices. Among the major features of iOS 5 was iCloud, a new cloud-based service for backing up the iPad and iPhone, and enhancements to mail and messaging, including Twitter integration into the operating system.
iOS 5 also included iMessage, which allows free messaging between iOS devices. And the new notification center allows a central repository for email messages, text messages, push notifications, missed calls and other events and alerts.