IOS

iOS is a series of mobile operating systems developed by Apple for their mobile device platforms (iPhone, iPod, and iPad). It was originally or formerly called iPhone OS and introduced alongside the 1st generation iPhone. The name stayed until the release of the iPad in early 2010 when Apple rebranded it to iOS. In 2019, Apple began to use the iPadOS moniker to brand the version of the operating system used on iPad devices.

iOS is based on the codebase of macOS, formerly OS X, and shares the same kernel, filesystem, and binary formats. The userland of iOS is like that of macOS, but with a mobile-friendly design that is touchscreen and content-centric. iOS lacks direct access to the filesystem and is unable to run arbitrary code by default. The only distribution method for software officially allowed on iOS is the built-in App Store. Since the release of iOS 11 in 2017, iOS has only been compiled for 64-bit ARM-based processors. It only runs on the iOS platforms manufactured by Apple.

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 through iOS 10 was 32 and 64-bit compatible. However, iOS 11 dropped support for 32-bit ARM processors and corresponding binaries. iOS 11 was also the first version of iOS with only 64-bit support. iOS 7 was the first version of iOS to bring 64-bit support.

Until late 2020, Apple used the “Golden Master” or “GM” build. In late 2020, despite the COVID-19 pandemic, the “Golden Master” or “GM” build was replaced by or updated to the “Release Candidate” or “RC” build. Since late 2020, Apple has used the “Release Candidate” or “RC” build.

iPhone OS 1 through iOS 15 was compatible with both iPhone and iPod touch. However, unlike iOS 11, which dropped support for 32-bit apps, iOS 16 dropped support for iPod touch. iOS 16 is also the first version of iOS supported only on or by iPhone since iOS 11, which was the first version of iOS to support only 64-bit apps.

No official emulator that can run the retail version of iOS exists. However, Apple provides the iOS Simulator, which runs a modified build of iOS on top of macOS with output in a dedicated window. Unofficial emulators like Corellium and QEMU-T8030 can emulate iOS to an extent.