The iPhone 4S was introduced in 2011: it’s the fifth model of the iPhone series and has a 3.5-inch "Retina" display (960 x 640 pixels). The biggest new feature that arrived with the iPhone 4S was Siri voice recognition. The iPhone 4s is strongly reminiscent of the iPhone 4. Only the notches on the metal frame and the slight change in button locations can distinguish the two. The iPhone 4S arrived with iOS 5 and a dual-core A5 chip from Apple. The iSight camera takes images with 8 megapixels and video at 1080p. The iPhone 4S is available in black and white and is the first iPhone with 16, 32 or 64 GB of memory.