Mobile operating systems come in different types to support the varying capabilities of mobile devices. The major mobile operating systems discussed are Symbian OS, Windows Mobile OS, Android OS, and iPhone OS. Symbian OS is 32-bit and runs on ARM architecture, while Windows Mobile has had several versions supporting pocket PCs and smartphones. Android OS is an open source platform based on Linux and developed by Google and OHA. iPhone OS, now called iOS, is Apple's proprietary operating system used in iPhones and iPads. Each operating system has distinct features and suits different types of mobile devices.