IPhone OS 1

iPhone OS 1, retroactively referred to as iOS 1, was the first major version of iOS to be publicly released by Apple. Launched on June 29, 2007, it is the mobile operating system that was developed from Mac OS X for use on first generation iPod touches and first-generation iPhones.

Similarities through iOS 5
iPhone OS 1 is very similar to iOS 4 and 5. It lacked many features, such as Notification Center, Multitasking and Reminders. The user interface was different, with the the lack of a 3D-like dock, the lack of an App Store, and no home screen wallpapers. The OS was faster and simpler than today's, but at the time it was considered revolutionary.

Trivia

 * This was originally called iPhone OS 1.0.
 * Before the name iPhone OS, Apple said the iPhone runs a version of OS X.
 * This is the first iOS to feature its first-ever firmware.
 * This is also the first iOS to feature iTunes.
 * iTunes was first featured on iPhone OS 1.1.1.