iOS 4
iOS 4 is the fourth major release of the iOS mobile operating system developed by Apple Inc. for its iPhone, iPod Touch, and iPad devices, initially previewed as iPhone OS 4 on April 8, 2010, before being renamed iOS 4 on June 7, 2010, to encompass its broader ecosystem beyond just the iPhone.[1][2] Released to the public on June 21, 2010—three days before the iPhone 4 debut—it marked a pivotal update by introducing over 100 new features, including true multitasking for third-party apps, customizable home screen folders, and enhanced enterprise support, while requiring devices like the iPhone 3GS or later for full functionality.[3] The update emphasized productivity and user experience enhancements, such as a unified inbox for multiple email accounts with threaded conversations, wallpaper customization for the home screen, and improved Safari with faster rendering and on-page search.[1][3] It also debuted Apple's iAd platform for in-app advertising without leaving apps, alongside the iBooks app and store for iPad users, and previewed Game Center for social gaming features like leaderboards and multiplayer matchmaking, which launched later in 2010.[1] Multitasking was limited to seven background services—such as VoIP, audio playback, and location updates—to preserve battery life on older hardware, while newer devices gained access to app switching via a double-tap of the home button.[3] iOS 4 supported the iPhone 3G and later, iPod Touch 2nd generation and later (with limitations on multitasking for pre-3rd gen models), and the original iPad, though some features like iBooks were iPad-exclusive at launch.[1][3] The version family extended through incremental updates, including iOS 4.1 in September 2010 (adding Game Center, HDR photos, and faster animations), iOS 4.2 in November 2010 (unifying iPad and iPhone features with AirPlay and AirPrint), and iOS 4.3 in March 2011 (introducing personal hotspot and AirPlay mirroring), before being succeeded by iOS 5 in 2011.[3] These releases collectively over 1,500 new APIs for developers, fostering richer app ecosystems while prioritizing security and performance.[1]Development and announcement
Development process
Development of iOS 4 commenced in late 2009, immediately following the release of iPhone OS 3.1 in September 2009, with a primary focus on porting select iPad features to the iPhone platform and implementing native multitasking support.[4] This timeline aligned with early prototyping efforts for the accompanying iPhone 4 hardware, where initial iOS 4 builds were integrated to test core system behaviors.[5] The engineering objectives centered on enhancing third-party app functionality through limited background processing, all while preserving device battery efficiency and smooth operation on resource-constrained models like the iPhone 3G.[1] These priorities addressed longstanding user demands for productivity tools without sacrificing the responsive user experience that defined prior iPhone OS versions. Multitasking, in particular, required innovative API restrictions to mitigate performance impacts. Cross-team collaboration was essential, uniting iPhone and iPad software engineers under Scott Forstall's leadership to consolidate and adapt the underlying OS framework for shared compatibility.[6] This unification effort streamlined code sharing, reducing redundancy and enabling faster iteration on device-agnostic components. Throughout the process, internal beta distributions were conducted to evaluate system stability across compatible hardware, with rigorous emphasis on memory allocation and garbage collection optimizations to prevent crashes or slowdowns during background operations.[7]Public announcement
iOS 4 was publicly announced on April 8, 2010, at Apple's special media event held at its Cupertino headquarters, positioned as the successor to iPhone OS 3.[1] The event, attended by journalists and developers, featured a keynote by Apple CEO Steve Jobs, who unveiled over 100 new user features and more than 1,500 new APIs for the upcoming operating system update.[1] Initially presented under the name iPhone OS 4, it was later rebranded as iOS 4 during Apple's Worldwide Developers Conference on June 7, 2010, to emphasize its expanded support across Apple's ecosystem, including the iPhone, iPod Touch, and iPad.[8] During the presentation, Jobs emphasized two flagship additions: true multitasking for third-party applications, enabling background execution for tasks like audio playback and VoIP calls while optimizing battery life, and folders for organizing home screen icons by dragging one app onto another, potentially accommodating over 2,000 apps.[1] He demonstrated these features live, highlighting how they addressed longstanding user requests for improved productivity and interface efficiency on mobile devices.[9] The keynote also provided previews of several user interface refinements, including a unified inbox that aggregates email from multiple accounts with threaded conversations and direct attachment support, customizable wallpapers for the home and lock screens selectable from built-in options or personal photos, and Bluetooth keyboard compatibility for enhanced input on supported devices.[1][9] These teasers underscored Apple's focus on making the platform more versatile and iPad-aligned, with a beta version made available to developers immediately following the event for testing ahead of the summer release.[1]Release and versions
Initial release
iOS 4.0 was initially released to the public on June 21, 2010, as a free software update distributed via iTunes for compatible devices including the iPhone 3GS, iPhone 3G, third-generation iPod Touch, and second-generation iPod Touch.[8] The update required iTunes 9.2 or later and had a download size of approximately 300 MB, depending on the device model.[10] Adoption of the update was rapid in the weeks following launch, with analytics showing that more than 50% of active iPhone users had installed iOS 4 by late July 2010.[11] Support for the iPad was not included in the initial iOS 4.0 release, as the device had launched earlier in April 2010 with iPhone OS 3.2; iPad users gained access to iOS 4 features starting with the iOS 4.2 update in November 2010.[12]Major updates
iOS 4.1, released on September 8, 2010, addressed significant battery drain issues reported in the initial iOS 4.0 rollout, alongside performance improvements for older devices like the iPhone 3G.[13] It introduced Game Center, Apple's social gaming network that allowed users to compete with friends, track achievements, and discover leaderboards across compatible apps. Additionally, the update enabled direct Wi-Fi uploading of high-definition (HD) videos recorded on the iPhone 4 to services like YouTube and MobileMe, enhancing content sharing without quality loss.[14] iOS 4.2, released on November 22, 2010, extended core iOS 4 features to the iPad for the first time, with the iPad version appearing as 4.2.1 in the user interface due to minor build differences.[15] It introduced AirPlay for wireless streaming of audio, video, and photos to Apple TV, and AirPrint for direct printing to compatible printers without needing additional software.[12] The update also refined multitasking on the iPad, providing faster app switching and background app refresh tailored to the device's larger screen and hardware. iOS 4.3, released on March 9, 2011, brought further refinements including Personal Hotspot, allowing iPhone 4 users to share their cellular data connection via Wi-Fi, Bluetooth, or USB with up to five devices.[16] It added a Safari Reading List for saving web pages for offline viewing and improved overall system animations for smoother transitions and reduced latency. This version marked the end of major feature updates for the iPhone 3G and second-generation iPod Touch, as subsequent releases dropped support for those devices, though earlier versions like iOS 4.2.1 continued to receive security patches where applicable.[17] Security updates for iOS 4 devices continued beyond the major releases for supported hardware, with the final update for older devices like the iPhone 3G and second-generation iPod Touch being iOS 4.2.1, released on November 22, 2010.[12]Features
User interface enhancements
iOS 4 introduced several enhancements to the user interface, improving personalization, navigation, and input methods across compatible devices. These changes focused on making the operating system more intuitive and visually appealing, allowing users greater control over their device's appearance and interaction flow. Key updates included options for customizing the visual backdrop of screens and refining how users access and manage content within built-in applications. One prominent addition was the ability to set customizable wallpapers for both the lock screen and home screen. Users could select from pre-installed images provided by Apple or import personal photos synced from their computer via iTunes. To apply a wallpaper, users navigated to Settings > Wallpaper, chose an image or album, adjusted its position and scale, and assigned it to one or both screens. This feature enhanced the device's aesthetic personalization across all compatible devices.[18] The Mail application received a unified inbox, which aggregated messages from multiple email accounts into a single view for streamlined access. Tapping "All Inboxes" on the Mailboxes screen displayed incoming emails from accounts like MobileMe, Microsoft Exchange, or other popular providers in one consolidated list, reducing the need to switch between accounts manually. This update improved overall email management efficiency.[1][18] Support for external Bluetooth keyboards was added to facilitate faster text input, particularly for productivity tasks. Compatible devices, including the Apple Wireless Keyboard, could be paired through Settings > General > Bluetooth, enabling wireless typing across apps like Mail and Notes. This enhancement was especially useful for users composing longer messages or documents on the go.[7][18] iOS 4 also incorporated an emoji keyboard for adding expressive icons to messages and other text fields. Accessible via international keyboard settings under General > Keyboard > International Keyboards > Add New Keyboard > Emoji, it provided a dedicated layout for symbols, particularly prominent on Japanese iPhone models but available globally. Users could switch to it during typing for enhanced communication in apps like Messages.[18] Additionally, folders for app organization were introduced, enabling users to drag one icon onto another to create customizable groups, which briefly ties into broader navigation improvements without altering core UI aesthetics.[18]Multitasking and background processes
iOS 4 marked the first introduction of multitasking capabilities to the iPhone operating system, allowing users to switch between applications without fully closing them and enabling select background processes to continue running. This feature addressed long-standing user demands for improved productivity on mobile devices, while prioritizing battery life and performance through a suspend-and-resume model rather than true concurrent execution for most apps. Users access the multitasking interface by double-clicking the Home button, which reveals a horizontal tray displaying icons and snapshots of recently used applications at the bottom of the screen. Swiping left or right navigates through the tray, and tapping an icon brings the corresponding app to the foreground, resuming it from its previous state. The system supports maintaining multiple apps in this suspended state, though the practical limit depends on available RAM; the system automatically purges older ones to free memory when necessary.[19][20] Beyond simple switching, iOS 4 permitted specific types of background execution for third-party apps, including audio playback (such as music or streaming), Voice over IP (VoIP) services for calls, location updates for navigation or tracking, and local notifications to alert users without foreground activity. Developers enabled these by declaring the appropriate modes in the app's Info.plist file, such as "audio" for background sound or "voip" for telephony. Additionally, apps could request finite background time (up to about 10 minutes) to complete tasks like downloading content after transitioning to the background. These capabilities were designed to support essential functions without excessive resource use.[21][22] A core mechanism enabling efficient switching was fast app switching, where backgrounded apps entered a suspended state: the system captured a snapshot of the app's interface for visual representation in the switcher and preserved its memory state on disk without ongoing CPU execution. Upon reactivation, the app resumed nearly instantaneously from this saved state, avoiding the need for a full reload and minimizing launch times to under a second in most cases. This approach ensured a responsive user experience while conserving power, as suspended apps consumed no battery.[23][24] Full multitasking was available only on devices with sufficient hardware, specifically the iPhone 3GS and later models, iPod touch 3rd generation and later, and the original iPad; the iPhone 3G and iPod touch 2nd generation supported iOS 4 but lacked true multitasking, limiting them to basic background audio playback while terminating other apps upon switching. Developers could detect support via theUIApplication class's isMultitaskingSupported property to adapt behavior accordingly.[25][3]
To optimize battery life, iOS 4 automatically suspended inactive background apps after a short period, halting all execution except for approved modes like audio or location; apps were encouraged to release unnecessary resources during suspension to avoid system-forced termination under low memory conditions. This design balanced functionality with the constraints of mobile hardware, preventing the rapid battery drain seen in full desktop-style multitasking.[21]