The iPhone 4S had the same design as the iPhone 4, but has several new features such as an upgrade to the Apple A5 processor, and an 8 MP camera with 1080p video recording. It shipped with iOS 5, which is the fifth major version of Apple's mobile operating system, iOS. It had new features such as iCloud, iMessage, Notification Center, Reminders, and integration with Twitter. It also had a voice activation system named Siri that was included in later generations of mobile Apple products.