OS 4.0: Implications for Developers and for You

The release of Apple's newest operating system for the iPhone, iPad, and Touch devices was introduced with 1500 new APIs for developers to explore. When expanding the platform, Apple identified "tent poles" of functionality necessary to support a richer app experience. The iPhone SDK 4 arrives with seven new tent pole features for users and services for developers. Much like the release of OS 3, Apple has maintained compatibility of the new OS to all Touch platforms while limiting some of the new functionality to Gen 3 hardware.

Developers receive the new iPhone OS 4 with all the APIs necessary to take their 185,000+ apps to the next level. In an apparent goal to keep what is good about a single threaded environment, Apple tried to expand only where the iPhone OS 3.2 constraints hurt them. The seven new multitasking services exist because Apple maintains that developers do not need unrestrained multitasking as much as they need an API toolset with a wider canopy to work under. To demonstrate these new capabilities, Steve Jobs and his supporting cast highlighted the new Multitasking APIs with improved versions of previously constrained apps.


The first tent pole in the iPhone OS 4 API is VoIP. The iPhone's combination of wireless Ethernet and 3G data services has proven an effective pairing of IP connectivity technologies. In the introduction of OS 4, Apple demonstrated how the telephony company Skype (free; app2.me/2378) was able to use the new VoIP service to overcome their iPhone app's biggest hurdle. When re-factored to use the new APIs, an improved Skype app can alert the user of an incoming call even when the app has been exited. Extending VoIP capabilities gives telephony and instant messenger apps the ability to deliver more robust communication solutions on Apple's mobile platforms.


Historically only Apple's applications could output audio when they were not open. The new background audio service exposes this precious functionality to third-party app developers, empowering their apps with the ability to output audio much like Apple's iPod app has done since the first generation of iPhones. One of the most notable companies impacted by this is Pandora (free; app2.me/2410), whose member base increased 30,000 users per day after rolling out their iPhone app. Tens of thousands of users have enjoyed Pandora's music streaming but only while the app was running. Once an incoming phone call occurred, the Pandora app exited and the music stopped.

Fast app switching and Task finishing

The Application Dock makes its first appearance in iPhone OS 4. The Dock is accessible by a double tap of the home button, providing the end-user with an ability to switch between active applications. Apps targeting the new OS can be written to resume execution rather than using cumbersome techniques to reload settings from a previous execution. The suspended app does not consume CPU cycles, but users will be able to move throughout other apps while any lengthy compilation tasks complete. The Task finishing service makes it possible for suspended apps to keep a compilation task going in the background.

Push and Local Notifications

iPhone OS 3 included the first version of Push Notifications. By utilizing Apple's servers, developers have since pushed over 1 billion notifications from their apps. In OS 4, Apple made the Local Notifications API a tent pole service. At the most basic level, the new service provides a mechanism for VoIP apps to alert users of an incoming call. It also provides alarm clock style apps with a method of sounding alarms even after the app has been exited. Ultimately this will open the door for developers to utilize local notifications and the Fast app switching service to enrich the users' experiences throughout everyday apps.


Keeping "free apps free" received focus during the expansion of the platform services. Apple has launched iAd and the supporting API set in recognition that no software is developed without someone investing time and effort. The iAd content is delivered in HTML 5 and allows for full screen display within an app. Other ad functionality includes the ability to display videos and buy an app from within the ad. Apple has set up a revenue stream for developers by marketing the iAd platform to advertisers and then splitting the ad revenue 40/60 with the developers choosing to utilize the service.

The new "tent pole" services strengthened the iPhone platform architecture in OS 4. Some of the new services will expand the general capabilities of everyday apps. Others will give applications like Skype and Loopt (free; app2.me/2423) the ability to meet many of their users' biggest complaints. The iPhone SDK 4 APIs give social networking applications an opportunity to utilize low power draw location services and empower turn-by-turn navigations apps the high power drain capabilities of precision GPS.

What do these 1500 new APIs give us?
Summer 2010
Creating Apps
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