IOS 4

iOS 4 is the fourth major release of the iOS mobile operating system developed by Apple Inc., being the successor to iPhone OS 3. It was announced at the Apple Special Event on April 8, 2010, and released on June 21, 2010. iOS 4 was the first version branded as "iOS" rather than "iPhone OS", due to the release of the iPad. It was succeeded by iOS 5 on October 12, 2011.

iOS 4 introduced many features that have since become commonplace, such as folders on the home screen, significantly increasing the number of apps that can be displayed. Support for home screen wallpapers on the iPhone was also added, although limited to newer devices due to animation performance requirements. The operating system also added a multitasking feature, letting apps dealing with Internet calling, location and audio playback function in the background, whereas a similar but more restricted "Fast App Switching" technology enabled any app to be left inactive in the background while users switch to other apps. iOS 4 also added a system-wide spell checking feature, enabled iBooks on iPhone, unified the Mail inbox to combine content from different email providers, and introduced both Game Center for social gaming and FaceTime for video calling.

The iOS 4 update introduced performance and battery problems on iPhone 3G devices, with Apple investigating the matter and promising then-upcoming updates. However, the company became the subject of a lawsuit from an unsatisfied customer over the issues. Around the same time, the release of iPhone 4 and its subsequent antenna problems made Apple focus on unsuccessfully attempting to patch the issues with software updates.

iOS 4 is the final version of iOS that features the iPod app for music and videos on iPhones. Starting with iOS 5, iPhones do not have the iPod app, but instead have the Music and Videos apps, as the iPod Touch and iPad do. It is also the last version of iOS that supports the iPhone 3G and second-generation iPod Touch, up to version 4.2.1 (4.3 dropped support for both devices).

Apps

 * iBooks
 * Game Center
 * FaceTime

History
iPhone OS 4 was introduced at the Apple Special Event on April 8, 2010. At the WWDC keynote address on June 7, 2010, it was renamed to iOS 4 in order to be more inclusive to the iPod Touch and iPad.

iOS 4 was officially released on June 21, 2010.

Home screen
iOS 4 raised the maximum number of home screen apps from 180 to 2,160 due to the addition of folders. These folders would automatically be named based on the containing apps' respective App Store category. On the iPhone, the ability to choose wallpapers and see them on the home screen was also added, though the feature was notably absent from iPhone 3G and the second-generation iPod Touch due to poor performance of icon animations. Additionally, the iPhone's dock was updated to be skeuomorphic, as with the Dock on the iPad and Mac OS X, and no longer has a grey line underneath it; the icons were redesigned to match.

Multitasking
iOS 4 introduced multitasking. The feature allowed users to switch between apps instantly by clicking the home button two times. It was implemented in such a way that did not cause excessive battery drain. Multitasking was limited to apps dealing with Internet calling, location, and audio playback, while a similar "Fast App Switching" technology meant users could leave an app and enter another, with the original app remaining in the background until the user returns. This feature was notably absent from iPhone 3G and the second-generation iPod Touch due to performance issues. iOS 4 introduced a spell checking feature that underlined misspelled words in red. Tapping on the word would provide a pop-up with a recommended replacement.

Camera
The Camera app now supports 5x digital zoom.

iOS 4 introduced iPhone and iPod Touch support in iBooks, which was already included on the iPad. Though not a default app, it was available through the App Store.

The Mail app featured a unified inbox on iOS 4, allowing users to see messages from all of their email accounts displayed together in a single inbox. It also gained support for MobileMe e-mail aliases and multiple Exchange accounts for business users.

iOS 4 added a new app called Game Center, an online multiplayer social gaming network, which allows users to invite friends to play games and to compare their scores on a leaderboard. It was not available on the iPhone 3G.

FaceTime
iOS 4 introduced FaceTime, a videotelephony app that uses the device's camera to allow the user to make video calls with other FaceTime users. This feature was absent from the iPhone 3G, second-generation iPod Touch, iPhone 3GS, and third-generation iPod Touch due to the lack of required features, such as a front-facing camera.

Safari
The Safari mobile web browser on iOS 4 added Bing as a search option in addition to Google and Yahoo!. Beginning with iOS 4.2.1, specific words or phrases on a page could be searched.

Performance and battery issues
iPhone 3G users reported performance and battery issues after upgrading to iOS 4. Apple started an investigation of the matter in July 2010. In November, Apple was sued for the issues, with an unsatisfied customer alleging "violating the Consumer Legal Remedies Act, unfair business practices, and false and deceptive advertising", with further allegations that Apple knew its software would cause problems on older models. Apple never responded to the allegations, but wrote in a reply to another unsatisfied customer in August 2010 that updates were "coming soon".

Alarm clock
In all versions of iOS 4, the alarm clock in the clock app had a problem in DST when it would go off an hour too early or too late.

Antenna problems
Upon its release, some iPhone 4 users reported having technical problems with the phone's antennas. Apple attempted to fix the issue in software with iOS 4.0.1, but failed to do so.

Supported devices
iOS 4 drops support for the first-generation iPhone and first-generation iPod Touch due to hardware limitations, though the iPhone 3G did support iOS 4, despite it having the same processor as the first-generation iPhone. However, the iPhone 3G and iPod Touch (2nd generation) have limited support

iPhone

 * iPhone 3G
 * iPhone 3GS
 * iPhone 4

iPod Touch

 * iPod Touch (2nd generation)
 * iPod Touch (3rd generation)
 * iPod Touch (4th generation)

iPad

 * iPad (1st generation)
 * iPad 2

Apple TV

 * Apple TV (2nd generation)