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 company's Worldwide Developers Conference on June 7, 2010, and was released on June 21, 2010. iOS 4 is the first iOS version issued under the "iOS" rebranding, dropping the "iPhone OS" naming convention of previous versions. It was succeeded by iOS 5 on October 12, 2011.
iOS 4 introduced folders on the home screen, significantly increasing the number of apps that can be displayed. Support for custom wallpapers 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.
History.
iOS 4 was introduced at the Apple Worldwide Developers Conference keynote address on June 7, 2010. Notably, it was the first iOS release to be named simply "iOS", ending the "iPhone OS" naming pattern of previous versions.
iOS 4 was officially released on June 21, 2010.
System features.
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. The ability to add custom wallpapers to 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.
Multitasking.
iOS 4 introduced multitasking. The feature allowed users to switch between apps instantly by double-clicking the home button. 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.
Spell check.
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 could take pictures with 5x digital zoom.
App features.
iBooks.
iOS 4 introduced iPhone and iPod Touch support in iBooks, which was already included on iPad. Though not a default app, it was available through App Store.
Mail.
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.
Game Center.
iOS 4.1 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.
Problems.
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 with iOS 4.0.1, but failed to do so.
Supported devices.
The first-generation iPhone and the first-generation iPod Touch cannot run iOS 4 and above due to hardware limitations. This marked the first time Apple dropped support for older devices.