# 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 and iPads. Starting with iOS 5, iPhones and iPads do not have the iPod app, but instead have the Music and Videos apps, as the iPod Touch does. 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), due to hardware and performance issues.

## Apps

* iBooks
* Game Center
* FaceTime

## History

iOS 4 was introduced at the Apple Special Event on April 8, 2010. At the WWDC keynote address on June 7, 2010, it was named iOS 4 and not iPhone OS 4 in order to be more inclusive to the iPod Touch and iPad.
iOS 4 was officially released on June 21, 2010.

## System features
### Folders

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.

### 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.

### Apps

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.

### Fetures added on the iPhone inherited from the iPad

On the iPhone, the ability to choose wallpapers and see them on the home screen was also added, and the iPad had its ones replaced to be consistent, though the feature was notably absent from iPhone 3G and the second-generation iPod Touch due to poor performance of icon animations.
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.
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.

## 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 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

## Version history

| Version | Build | Codename | Release date | Notes | Update type |
| 4.0 | 8A293 | Apex | June 21, 2010 | Initial release for iPhone 4 GSM Allows use of multiple Mail inboxes Adds support for folders for app organization Allows creation of music playlists Introduces the iBooks app Adds tap-to-focus in the Camera app Allows uses of Bluetooth keyboards Allows users to gift apps to other Apple IDs in the App Store, as long as those apps contained no fraudulent information Adds spellcheck iPhone 3GS and iPhone 4 only: Adds support for multitasking Adds support for setting a home screen wallpaper iPhone 4 only: LED flash for camera 5x digital camera zoom FaceTime | Initial Release |
| 4.0.1 | 8A306 | Apex | July 15, 2010 | Only for iPhones Changes the algorithm that displays cellular signal strength after Antennagate Fixes a bug with Microsoft Exchange accounts | Bug Fixes |
| 4.0.2 | 8A400 | Apex | August 11, 2010 | Fixes a bug that allowed a maliciously crafted PDF to lead to arbitrary code execution Fixes a bug that allows code running as user to gain system privileges Due to all these patches, JailbreakMe 2.0 stops working. | Bug Fixes |
| 4.1 | 8B117 8B118 | Baker | September 8, 2010 | Initial release on iPod Touch (4th generation) Adds HDR photo capture support to the iPhone 4 Allows upload of high definition videos captured on the iPhone 4 to YouTube and MobileMe Fixes a bug that allowed a maliciously crafted .tiff image to lead to arbitrary code execution Fixes a bug that allowed an attacker in a privileged network position to redirect FaceTime calls Fixes multiple bugs that caused visiting a maliciously crafted website to lead to arbitrary code execution Exclusive to iPhone 3GS, iPhone 4, and iPod touch (3rd generation): Game Center, a service that allows syncing of game save data, achievements, and more. Game Center had previously been part of developer versions of iOS 4. | Feature Update |
| 4.2 | 8C134 | Unknown | November 1, 2010 | Adds AirPlay, allowing devices to stream audio or video to the Apple TV (1st generation) Adds AirPrint, allowing devices to print wirelessly to some HP ePrint printers Allows users to create a free MobileMe account to access Find My iPhone, which allows location tracking and remote locking or wiping of a device Adds support for the iPad (1st generation) Birthdays calendar does not display birthdays starting more than 77 years ago. Fixes glitch that can let a user get into the Phone app while the phone is locked via "Emergency Call" by dialing a random number and quickly pressing the lock button after dialing that call. Improved iPhone 3G and iPod Touch (2nd generation) performance. Import .ics calendar files directly for events. Improved battery performance. Birthdays icon has been changed in the Calendar app. Text search on web pages. (iPhone 3GS and iPod touch 3 and 4 only) 2 new fonts for Notes in Settings (Helvetica and Chalkboard). Added support for Chinese URL over Safari. Added an indicator in the App Store which shows if an app supports Game Center. Support for CoreMIDI. YouTube voting. Minor improvements in UI graphics. New parental controls for deleting apps, changing mail accounts and location services. The font size of text in Calendar can now be changed in the Accessibility settings. Fixes Voice over IP (VoIP) issues. Find My iPhone location feature is free (iPhone 4, iPod Touch (4th generation), and iPad) running on iOS 4.2.1. More than 30 new keyboards and dictionaries, including Arabic, Greek, and Hebrew. New animation for Multitasking. New bookmarks design (iPhone and iPod Touch only). New Voice Memos icon. Ability to initiate FaceTime calls from Voice Control. (iPhone 4 only) FaceTime shortcut from Messages app (iPhone 4 only). New text tone alerts (New and Original tone lists) (iPhone 4 only). Ringer and alerts on/off switch (Settings > Sounds) for volume buttons (iPhone only). Assign different text tone alerts to each contact. | Feature Update |
| 4.2.1 | 8C148 8C148a | Jasper | November 22, 2010 | Last version of iOS to run on iPhone 3G and iPod Touch (2nd generation) due to hardware and performance issues. Replaces iOS 4.2 as iOS 4.2 prevented Wi-Fi from working on the iPad (1st generation), iOS 4.2 was later pulled from public view | Bug Fixes |
| All devices except for iPhone 4 (CDMA) ||||||
| 4.3 | 8F190 8F191 | Durango | March 4, 2011 | Initial release on iPad 2 Adds personal hotspot to the iPhone 4 (GSM) Introduces iTunes home sharing Improves AirPlay Fixes multiple vulnerabilities in FreeType Fixes multiple bugs that caused viewing maliciously crafted .tiff images to lead to arbitrary code execution Fixes many, many bugs in WebKit that caused viewing a maliciously crafted website to lead to arbitrary code execution Fixes a bug that allowed an attacker connected to the same network as an iPhone to be able to trigger a remote reset | Initial Release, Feature Update |
| 4.3.1 | 8G4 | Durango | March 25, 2011 | Fixes iPod touch screen glitches Fixes bugs that prevented activation and connection of iPhones Fixes image flicker when using Apple Digital AV Adapter Updates SSL certificates after fraudulent certificates were issued by a Comodo affiliate registration authority Fixes multiple bugs that caused viewing of a maliciously crafted website to lead to arbitrary code execution | Bug Fixes |
| 4.3.2 | 8H7 8H8 | Durango | April 14, 2011 | Fixes a bug that caused FaceTime calls to freeze Fixes connectivity issues on cellular-equipped iPads Updates SSL certificates after fraudulent certificates were issued by a Comodo affiliate registration authority Fixes multiple bugs that caused viewing of a maliciously crafted website to lead to arbitrary code execution | Bug Fixes |
| 4.3.3 | 8J2 | Durango | May 4, 2011 | Fixes a bug that caused location to be reported incorrectly | Bug Fixes |
| 4.3.4 | 8K2 | Durango | July 15, 2011 | Fixes bugs that caused viewing a maliciously crafted PDF to cause arbitrary code execution Fixes a bug that caused code running as user to gain system privileges It also patches the latest version of JailbreakMe (JailbreakMe 3.0). | Bug Fixes |
| 4.3.5 | 8L1 | Durango | July 25, 2011 | Fixes a bug that allowed an attacker in a privileged network position to capture and/or modify data in SSL/TLS-protected network sessions | Bug Fixes |
| iPhone 4 (CDMA) only ||||||
| 4.2.5 | 8E128 | Unknown | January 11, 2011 | Preview release on iPhone 4 (CDMA). Only available to reviewers, never shipped on release devices Adds personal Wi-Fi hotspot support | Preview Release |
| 4.2.6 | 8E200 | Phoenix | January 31, 2011 | Initial release on iPhone 4 (CDMA), as while 4.2.5 also came with the device, 4.2.6 was the first public version. Bug fixes for personal hotspots | Initial Release |
| 4.2.7 | 8E303 | Phoenix | April 14, 2011 | Fixes a bug that caused FaceTime calls to freeze Updates SSL certificates after fraudulent certificates were issued by a Comodo affiliate registration authority Fixes multiple bugs that caused viewing of a maliciously crafted website to lead to arbitrary code execution | Bug Fixes |
| 4.2.8 | 8E401 | Phoenix | May 4, 2011 | Fixes a bug that caused location to be reported incorrectly | Bug Fixes |
| 4.2.9 | 8E501 | Phoenix | July 15, 2011 | Fixes bugs that caused viewing a maliciously crafted PDF to cause arbitrary code execution Fixes a bug that caused code running as user to gain system privileges It also patches the latest version of JailbreakMe (JailbreakMe 3.0). | Bug Fixes |
| 4.2.10 | 8E600 | Phoenix | July 25, 2011 | Fixes a bug that allowed an attacker in a privileged network position to capture and/or modify data in SSL/TLS-protected network sessions | Bug Fixes |
* ↑ Multitasking, home screen wallpapers and Bluetooth keyboard support are not available on both the iPhone 3G and iPod Touch (2nd generation), while Game Center, Apple's gaming network, was available on the iPod Touch (2nd generation) but not on the iPhone 3G.
* ↑ iPod Touch (4th generation) only
* ↑ No public release of iOS 4.2 is available, due to an issue that impacted Wi-Fi functionality on the iPad.
* ↑ iPhone 3GS only
* ↑ iPad 2 only
* ↑ iPad 2 (CDMA) only