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 5S and iPhone 5C were moved to the mid and low end of the iPhone range, respectively; the iPhone 5S still had 16 or 32 GB storage available while the iPhone 5C had to make do with 8 GB storage with only 4.9GB available to the user after installing iOS 8. Furthermore, the 5C's polycarbonate exterior received a mixed reception and was seen as a cost-cutting downgrade compared to the iPhone 5's aluminum/glass case; the 5S retained the latter design and looked even more premium due its additional gold finish. As of 2015–16, there were still a significant number of customers