iOS

Switching applications

In iOS 4.0 to iOS 6.x, double-clicking the home button activates the application switcher. A scrollable dock-style interface appears from the bottom, moving the contents of the screen up. Choosing an icon switches to an application. To the far left are icons which function as music controls, a rotation lock, and on iOS 4.2 and above, a volume controller.

With the introduction of iOS 7, double-clicking the home button also activates the application switcher. However, unlike previous versions it displays screenshots of open applications on top of the icon and horizontal scrolling allows for browsing through previous apps, and it is possible to close applications by dragging them up, similar to how handled multiple cards.[93]

With the introduction of iOS 9, the application switcher received a significant visual change; while still retaining the card metaphor introduced in iOS 7, the application icon is smaller, and appears above the screenshot (which is now larger, due to the removal of "Recent and Favorite Contacts"), and each application "card" overlaps the other, forming a effect as the user scrolls. Now, instead of the home screen appearing at the leftmost of the application switcher, it appears rightmost., the application switcher receives a major redesign. In the iPad, the and app switcher are combined. The app switcher in the iPad can also be accessed by swiping up from the bottom. In the iPhone, the app switcher cannot be accessed if there are no apps in the .

Ending tasks

In iOS 4.0 to iOS 6.x, briefly holding the icons in the application switcher makes them "jiggle" (similarly to the homescreen) and allows the user to force quit the applications by tapping the red minus circle that appears at the corner of the app's icon.[95] Clearing applications from multitasking stayed the same from iOS 4.0 through 6.1.6, the last version of iOS 6.

As of iOS 7, the process has become faster and easier. In iOS 7, instead of holding the icons to close them, they are closed by simply swiping them upwards off the screen. Up to three apps can be cleared at a time compared to one in versions up to iOS 6.1.6.[96]

Task completion

Task completion allows apps to continue a certain task after the app has been suspended. As of iOS 4.0, apps can request up to ten minutes to complete a task in the background.[99] This doesn't extend to background up- and downloads though (e.g. if a user starts a download in one application, it won't finish if they switch away from the application).

Siri

Siri () is an integrated into iOS. The assistant uses voice queries and a to answer questions, make recommendations, and perform actions by delegating requests to a set of Internet services. The software adapts to users' individual language usages, searches, and preferences, with continuing use. Returned results are individualized.

Originally released as an app for iOS in February 2010, and then integrated into at its release in October 2011. At that time, the separate app was also removed from the iOS .[106]

Siri supports a wide range of user commands, including performing phone actions, checking basic information, scheduling events and reminders, handling device settings, searching the Internet, navigating areas, finding information on entertainment, and is able to engage with iOS-integrated apps. in 2016, Apple opened up limited third-party access to Siri, including third-party messaging apps, as well as payments, ride-sharing, and Internet calling apps. With the release of , Apple updated Siri's voices for more clear, human voices, it now supports follow-up questions and language translation, and additional third-party actions.

Game Center

Game Center is an "social gaming network" It allows users to "invite friends to play a game, start a multiplayer game through matchmaking, track their , and compare their high scores on a ." iOS 5 and above adds support for profile photos.[112]

Game Center was announced during an iOS 4 preview event hosted by Apple on April 8, 2010. A preview was released to registered Apple developers in August., iPhone 3GS, and iPod Touch 2nd generation through 4th generation. There is no support for the , and the (the latter two devices did not have Game Center because they did not get iOS 4).

The main hardware platform for iOS is the . iOS releases before can only be run on iOS devices with ARM processors ( and architectures). In 2013, was released with full support (which includes a native 64-bit kernel, libraries, drivers as well as all built-in applications), processors with the introduction of the chip.; All new apps submitted to the App Store with a deadline of February 2015, and all app updates submitted to the App Store with a deadline of June 1, 2015. drops support for all iOS devices with 32-bit ARM processors as well as 32-bit applications, making iOS 64-bit only.[123]

The iOS SDK () allows for the development of on iOS.

While originally developing prior to its unveiling in 2007, Apple's then- did not intend to let third-party developers build native apps for iOS, instead directing them to make for the . with Jobs announcing in October 2007 that Apple would have a software development kit available for developers by February 2008. The SDK was released on March 6, 2008.

The SDK is a free download for users of personal computers. PCs. It also contains an iPhone to mimic the look and feel of the device on the computer while developing.

Combined with , the iOS SDK helps developers write iOS apps using officially supported programming languages, including and .[135]

iOS is the second most popular mobile operating system in the world, after . Sales of iPads in recent years are also behind Android, while, by web use (a proxy for all use), iPads (using iOS) are still the most popular.[136]

By the middle of 2012, there were 410 million devices activated. 2014, said 800 million devices had been sold by June 2014.[138]

During Apple's quarterly earnings call in January 2015, the company announced that they had sold over one billion iOS devices since 2007.

By late 2011, iOS accounted for 60% of the market share for smartphones and tablets. and 27.6% of the tablet and two-in-one market. reported iOS was used on 23.18% of smartphones and 66.25% of tablets worldwide, measured by internet usage instead of sales.[144]

In the third quarter of 2015, research from Strategy Analytics showed that iOS adoption of the worldwide smartphone market was at a record low 12.1%, attributed to lackluster performance in China and Africa. Android accounted for 87.5% of the market, with Windows Phone and BlackBerry accounting for the rest.

Since its initial release, iOS has been subject to a variety of different hacks centered around adding functionality not allowed by Apple., the primary motive for jailbreaking was to bypass Apple's purchase mechanism for installing the App Store's native applications.); however, with each subsequent iOS update, previously un-patched jailbreak exploits are usually patched.[149]

Since the arrival of Apple's native iOS App Store, and—along with it—third-party applications, the general motives for jailbreaking have changed.

In 2010, the (EFF) successfully convinced the U.S. Copyright Office to allow an exemption to the general prohibition on circumvention of copyright protection systems under the (DMCA). The exemption allows jailbreaking of iPhones for the sole purpose of allowing legally obtained applications to be added to the iPhone. Unlocking an iPhone allows the iPhone to be used with any wireless carrier using the same GSM or CDMA technology for which the particular phone model was designed to operate.[154]

Initially most wireless carriers in the US did not allow iPhone owners to unlock it for use with other carriers. However AT&T allowed iPhone owners who have satisfied contract requirements to unlock their iPhone. but it is ultimately the sole discretion of the carrier to authorize the device to be unlocked. There are programs to remove SIM lock restrictions, but are not supported by Apple and most often not a permanent unlock – a soft-unlock.[159]

The closed and proprietary nature of iOS has garnered criticism, particularly by advocates such as the , computer engineer and activist , Internet-law specialist , and the who protested the iPad's introductory event and have targeted the iPad with their "" campaign. Competitor , via a PR spokesman, criticized Apple's control over its platform.[164]

At issue are restrictions imposed by the design of iOS, namely (DRM) intended to lock purchased media to Apple's platform, the development model (requiring a yearly subscription to distribute apps developed for the iOS), the centralized approval process for apps, as well as Apple's general control and lockdown of the platform itself. Particularly at issue is the ability for Apple to remotely disable or delete apps at will.

Some in the tech community have expressed concern that the locked-down iOS represents a growing trend in Apple's approach to computing, particularly Apple's shift away from machines that hobbyists can "tinker with" and note the potential for such restrictions to stifle software innovation.
Former developer protested against Apple's control over its hardware as a "horrible precedent" but praised iOS's of apps.[167]

The iOS kernel is the kernel of . The original iPhone OS (1.0) up to iPhone OS 3.1.3 used Darwin 9.0.0d1. iOS 4 was based on Darwin 10. iOS 5 was based on Darwin 11. iOS 6 was based on Darwin 13. iOS 7 and iOS 8 are based on Darwin 14. iOS 9 is based on Darwin 15. iOS 10 is based on Darwin 16. iOS 11 is based on Darwin 17. iOS 12 is based on Darwin 18. iOS 13 is based on Darwin 19.[168]

iOS utilizes many security features in both hardware and software. Below are summaries of the most prominent features.

Secure Boot

Before fully booting into iOS, there is low-level code that runs from the Boot . Its task is to verify that the Low-Level is signed by the Apple public before running it. This process is to ensure that no malicious or otherwise unauthorized software can be run on an iOS device. After the Low-Level Bootloader finishes its tasks, it runs the higher level bootloader, known as . If all goes well, iBoot will then proceed to load the iOS kernel as well as the rest of the operating system.[169]