iPhone OS is the operating system that runs on the iPhone and iPod touch. It is based on a variant of the same basic Mach kernel that is found in Mac OS X. iPhone OS includes the software component "Core Animation" from Mac OS X v10.5 which, together with the PowerVR MBX 3D hardware, is responsible for the smooth animations used in its user interface. The operating system takes up considerably less than half a GB of the device's total 8 GB or 16 GB storage. It is capable of supporting bundled and future applications from Apple, as well as applications written by third-party developers and published through the iTunes Store.

Like an iPod, the iPhone is managed with iTunes version 7.3 or later, which is compatible with Mac OS X version 10.4.10 or later, and 32-bit Windows XP or Vista. The release of iTunes 7.6 expanded this support to include 64-bit versions of XP and Vista, and a workaround has been discovered for previous 64-bit Windows operating systems.

The iPhone's applications cannot simply be copied from Mac OS X and have to be written and compiled specifically for the iPhone. Additionally, the Safari web browser supports web applications written with AJAX.

Applications

The photo display application

There are several applications located on the Home screen: Text (SMS messaging), Calendar, Photos, Camera, YouTube, Stocks, Maps (Google Maps), Weather, Clock, Calculator, Notes, Settings, and iTunes (store). Four other applications, docked at the base of the screen, delineate the iPhone's main purposes: Phone, Mail, Safari, and iPod.

The YouTube application streams videos over Wi-Fi, 2G, or 3G after encoding them using the open H.264 codec, to which YouTube has converted about 10,000 videos. As a result, the YouTube application on iPhone can currently view only a certain selection of videos from the site.

At WWDC 2007 on June 11, 2007 Apple announced that the iPhone would support third-party "applications" via the Safari web browser that share the look and feel of the iPhone interface. On October 17, 2007, Steve Jobs, in an open letter posted to Apple's "Hot News" weblog, announced that a software development kit (SDK) would be made available to third-party developers in February 2008. Due to security concerns and Jobs' praise of Nokia's digital signature system, it was suggested that Apple would adopt a similar method. The SDK has also allowed application development for the iPod touch. The iPhone SDK was officially announced on March 6, 2008, at the Apple Town Hall facility. The SDK will allow developers to develop native applications for the iPhone and iPod touch, as well as test them in an "iPhone simulator". However, loading an application onto the devices is only possible after paying a Apple Developer Connection membership fee. Developers are free to set any price for their applications to be distributed through the App Store, of which they will receive a 70 percent share. Developers can also opt to release the application for free and will not pay any costs to release or distribute the application beyond the membership fee. The SDK was made available immediately, while the launch of applications had to wait until the firmware update which was released on July 11, 2008. This update is free for iPhone users and there is a charge for iPod touch owners.

Once a developer has submitted his/her application to the App Store, Apple holds firm control over its distribution. For example, Apple can halt the distribution of applications it deems inappropriate as has happened with a $1000 program that has as sole purpose to demostrate the wealth of its user. More strikingly, Apple also installs a kill switch in the programs it distributes through the App store: all applications can be remotely disabled at Apple's command. The company considers it irresponsible not to have this kind of control over the software the user runs.

Many third-party Safari "applications" and un-signed native applications are also available. The ability to install native applications onto the iPhone outside of the App Store will not be supported by Apple. Such native applications could be broken by any software update, but Apple has stated it will not design software updates specifically to break native applications other than applications that perform SIM unlocking. As of September 15, 2008, iPhone software version 2.1 is still "exploitable" by the same method that enabled unsigned applications in software versions as early as version 1.1.3, indicating that Apple is making good on their promise not to intentionally cripple unofficial development.

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