iOS is a series of mobile operating systems developed by Apple for their mobile device platforms (iPhone, iPod, and iPad). It was initially known as iPhone OS and introduced alongside the 1st generation iPhone. The name would stay until the release of the iPad in 2010 when Apple rebranded it to iOS.
iOS is based on macOS's codebase and shares the same kernel, filesystem, and binary formats. The userland of iOS is similar to that of macOS, but with a mobile-friendly design that is touchscreen and content-centric. iOS lacks direct access to the filesystem and cannot run arbitrary code by default. The only distribution method for software officially allowed on iOS is the built-in App Store. As of 2017, iOS has only been compiled for ARM-based processors and only runs on the iOS platforms that Apple manufactures.
iOS's userland consists of a home screen (known as Springboard) that manages the user's applications. Many applications from macOS exist in iOS and vice-versa.
iPhone OS 1.0 through iOS 10 is 32 and 64-bit compatible, although iOS 11 dropped any support for 32-bit ARM processors and corresponding binaries.
No emulators exist that can run the retail version of iOS (compiled for ARM), however, Apple does provide the iOS Simulator which runs x86 builds of iOS on top of the macOS kernel (with output in a dedicated window).
|Name||Kernel Version||Codename||Release Date||Notes|
|iOS 4||Darwin 10.3.1||Apex (iOS 4) / Baker (iOS 4.1) / Jasper (iOS 4.2) / Phoenix (iOS 4.2.5 - 4.2.10) / Durango (iOS 4.3)||Released in June 2010.|
|iOS 5||Darwin 11||Telluride (iOS 5) / Hoodoo (iOS 5.1)||Released in October 2011.|
|iOS 6||Darwin 13||Sundance (iOS 6) / Brighton (iOS 6.1)||Released in September 2012.|
|iOS 7||Darwin 14||Innsbruck (iOS 7) / Sochi (iOS 7.1)||Released in September 2013.|
|iOS 8||Darwin 14||Okemo (iOS 8) / OkemoTaos (iOS 8.1) / OkemoZurs (iOS 8.2) / Stowe (iOS 8.3) / Copper (iOS 8.4)||Released in September 2014.|
|iOS 9||Darwin 15||Monarch (iOS 9) / Boulder (iOS 9.1) / Castlerock (iOS 9.2) / Eagle (iOS 9.3)||Released in September 2015.|
|iOS 10||Darwin 16||Whitetail (iOS 10) / Butler (iOS 10.1) / Corry (iOS 10.2) / Erie (iOS 10.3)||Released in September 2016.||Last version of iOS to have 32-bit ARM support.|
|iOS 11||Darwin 17||Tigris (iOS 11) / Bursa (iOS 11.1) / Cinar (iOS 11.2) / Dalaman (iOS 11.2.5 & 11.2.6) / Emet (iOS 11.3) / Fatsa (iOS 11.4)||Released in September 2017.||It is the first version of iOS to drop 32-bit ARM support.|
|iOS 12||Darwin 18||Hope (iOS 12)||Released on September 17, 2018.|