IPhone 4S announced iPhone 5s and iPhone 5c. This was unusual for Apple as an upper case 'S' had been used since the introduction of the iPhone 3GS in 2009. On September 9, 2014, the iPhone 4S was officially discontinued following the reveal of the iPhone 6 and the iPhone 6 Plus. However, 4S production did continue for developing markets until February 17, 2016. On June 13, 2016, following the release of iOS 10, Apple dropped support on the iPhone 4S, making iOS 9.3.5 the last version available for the device. The runs iOS, Apple's mobile operating system. The user interface of
IPhone screens on the first three generations have a resolution of 320×480 (HVGA) at 163 ppi; those on the iPhone 4 and iPhone 4S have a resolution of 640×960 at 326 ppi; the 4-inch models, with 640×1136 at 326 ppi; the 4.7-inch models, with 750×1334 at 326 ppi; the 5.5-inch models, with 1080×1920 at 401 ppi; and the 5.8-inch model X, with 1125×2436 at 458 ppi. The initial models were using twisted-nematic (TN) LCDs. Starting with iPhone 4, the technology was changed to in-plane switching (IPS) LCDs. The iPhone 5 model's screen results in an aspect ratio of approximately 16:9. The