iPhone OS 4 is the fourth generation of Apple's iPhone Operating System that powers their popular iPhone, iPod Touch, and iPad devices. With this iteration Apple responds to many of their critics in incorporating application multitasking and background processing. However, in true Apple fashion, they have devised their own take on these features that they claim preserves battery life and responsiveness while offering the ability to run and switch between multiple applications. This differs from a typical multi-tasking implementation as Apple created seven new services that the OS can run in the background and that 3rd party apps have access to, but the actual 3rd party apps are paused and resumed rather than concurrently executed. Alongside multitasking Apple introduces some other major functionality in iPhone OS 4, including a comprehensive gaming social network akin to Xbox Live, and a rich integrated ad platform called iAd. It must be noted that some functions such as multitasking are not compatible with iPhone versions older than the 3GS.
- limited background processing
- background audio - for apps like Pandora and Last.fm stream music while using other applications
- Voice over IP - for apps like Skype receive calls even when it's not open
- Background location - for apps like Loopt to automatically update your location
- Push notifications
- Local notifications
- Task completion - for apps like flickr to continue uploading a photo even after the app is closed
- Fast app switching
- change your homescreen wallpaper
- homescreen folders
- drag and drop apps on top of one another to automatically create app group folders
- enhanced mail app
- unifies inboxes
- view e-mails as conversations
- enhanced enterprise features
- cross game mobile social network (a la Xbox Live)
- in-app advertising platform that's run on the OS level. Let's you interact with ads without leaving an app
- more API functions for developers
To preserve battery life background applications are run in a limited state that can perform a limited set of functions that Apple claims are the most crucial. Switching between applications is accomplished through a mini-dock that comes up when you press the home button twice.
While programs are running in the background they have access to a limited set of core functionality. Specifically they can play music, start or continue Voice over IP calls, update location information, display notifications, and complete started tasks. Apple claims that these services will provide the key functionality that people want from the apps while not compromising battery life or performance.
The iAd platform is part of the core operating system. This means that apps can have rich, interactive advertisements that don't require you to leave the app. Apple claims that this will let people engage with the ads better, which will let developers monetize off their free applications better. The hope for end users is that there will be even more, and better quality free apps.