IPhone 4 models. In fall 2010, pentalobe screws started to replace the Philips screws used in post-repair units in the US and in production units in Japan. The iPhone 4 shipped with iOS 4, which was the newest version of Apple's iOS mobile operating system at the time. iOS 4 introduced a multitasking system, allowing apps to remain "suspended" in memory, perform certain operations in the background, and allowing users to switch between apps using an on-screen menu. It also introduced FaceTime, which allows users to perform video calls between other iPhone, iPad, iPod Touch, and OS X users. The iPhone 4
IPhone 5C polycarbonate housing, which is strengthened by a steel band. However, due to the material of design changes, the phone weighs 132 grams, which is 20 grams heavier than both the 5 and the 5S, but still lighter than older iPhone models. The design of the iPhone 5C is also considerably thicker but closely similar to the design of the iPod Touch (5th generation) models, which is also available in a variety of colors, but in a different coating finish. Other minor changes include a different camera assembly and the design of the mute/ringer switch. This iPhone received positive reviews for