It was announced on April 8, 2010, and released on June 21, 2010. This was the OS that finally got a name with a lowercase letter and an official trademarked registered name when the original, iPhone-only set of policies completed its transformation into iOS as Apple began to see itself using it on devices beyond just phones (the iPod touch and eventually iPad).

With the addition of iOS 4, some of the most demanded and basic features were introduced to the device IE: multitasking support, creation of app folders and a combined Mail inbox which made it better to use and enhanced productivity. This was a huge step forward and indicative of the quick rate at which iOS would develop as a mobile operating system.
Rebranding to iOS
iPhone OS was actually what the operating system of iOS 4. With this release:
Apple and rebranded it “iOS”, as the iPod touch got bigger, and eventually iPad (which received iOS 4.2.1 later in 2010).
It also felt more consistent with Apple focusing on cross-device experiences and one unified platform.
This has since been a pivotal change in the strategy of Apple’s ecosystem.
Multitasking: Finally, Real App Switching
The most anticipated feature, multitasking, was finally added in iOS 4–though only for devices with the A4 chip or better (such as the iPhone 4 and iPhone 3GS):
Permitted multitasking by enabling users to switch between apps without a restart, and added an app switcher with card-like views that was activated when double-pressing the Home button.
The multitasking support and other background functionality offered by APIs, including:
Audio playback (e.g., Pandora, Spotify).
VoIP (e.g., Skype).
Background location (e.g., Maps).
Background operation finishes (e.g download/upload).
So Apple it only allowed ‘specific’ background services to be kept alive — purely on battery life and performance grounds.
That small addition suddenly made iOS feel less like a simple, single-task environment and more like an actual computing platform.
Home Screen Folders — Bringing Order to the App Chaos
IOS 4 Series – Introduced app folders for the Home Screen, as more and more apps started ending up people’s devices:
That would result in the two apps you dragged together being combined into a folder iOS would auto-name using the category of app.
At first, each folder could contain up to 12 icons (120 on iPhone 5 and newer), although this number was expanded to 16 in iOS 7.
This was a major step in limiting the Home Screen chaos and added more clarity and customization.
It was all of a sudden folders joined the iOS experience and now you could nestle your most-used project management apps into a single directory.
Mail Inbox and Unified & Productivity Folders
MailiOS 4 got a complete Mail revamp, and with it came enhanced multi-account management:
Unified inbox (consolidating all email messages in one place)
Enabled conversation threading (emails are grouped by topic)
Bearbeiten Verbesserte Funktionen für Exchange, einschließlich der Unterstützung mehrerer Exchange-Accounts
These improvements contributed to making iPhones more suitable for business use and for advanced users.
iBooks & Apple’s iReading Campaign
iBooks (only available on iPad previously) — iOS 4 introduced iBooks which is Apple’s e-reader platform.
The app could be used to download books and PDFs directly from the iBookstore, then stored on a virtual bookshelf where they could be highlighted or annotated.
It also allowed users to import PDFs into the iBooks app for reading and archiving.
This hinted at a renewed focus on digital content and services by Apple.
FaceTime: Video Calling Over Wi-Fi
Introduced on iPhone 4 in iOS 4 FaceTime
Enabled FaceTime video calls over Wi-Fi between compatible Apple devices.
Built into the Phone and Contacts apps.
Introduced Apple Video Communication and later included on iPad, iPod touch, Mac.
FaceTime, in a way was the start of Apple’s apparent strict no-nonsense policy when it comes to secure, private and user-friendly communication from this day forward.
Custom Wallpapers and Visual Tweaks
iOS 4 was the first time that customers could set their own wallpaper on the Home Screen, not just on the Lock Screen;
This put in a more human element to the phone and was something that customers wanted from day one of the original iPhone.
The more refined and prettier icons, less reliance of shadows, and smoother animations are some minor UI enhancements in the entire system.
This indicated a strong trend towards user customization.
Performance and Device Compatibility
The first version of iOS 4 was compatible with the iPhone 3GS, iPhone 4 and iPod touch (3rd and 4th generations).
Although the 3G could technically run iOS 4, multitasking was disabled on it and the performance was terrible.
There are no updates for original iPhone (2G) and iPod touch (1st gen) devices, which cannot run iOS 4.
This was Apple’s first version of Mac OS X that placed limitations on what a specific piece of hardware could do — something the company would later make a trend for new versions.
Game Center (iOS 4.1)
Apple came up with a social gaming platform by the name of Game CenterWith iOS 4.1
When I was Dom, I could look at my achievements, compare them to his (he beat Horde mode in GoW3 before me), and if he had Xbox Live friends that also owned the game, invite them to multiplayer games.
While Game Center came to serve as the saucer of iOS gaming soup bowl, it was eventually deprecated along with its brethren in several future OS redesigns.
It was the blueprint for Apple’s investment in gaming going forward.
Near Future : AirPrint, AirPlay (iOS 4.2 / 4.2.1)
Released November 2010, iOS 4.2 unified Apple’s mobile devices with the tablet running the same OS for the fist time: New features included:
AirPrint – allows you to print wirelessly from your iOS device with supported printers.
AirPlay- Stream audio, video and photos Wirelessly to Apple TV or Wireless-enable speakers
Features Multitasking, and Folders to iOS for iPad
Called a major update, this took the iPad from the software side to part of the family.
iOS 4.x Updates
iOS 4.1 — Boosts iPhone 3G performance, adds HDR photography, launches Game Center
4.2.1: Only one unified iOS, with new features including AirPlay/AirPrint.
Debut of Personal Hotspot, Safari including the Nitro JavaScript engine and photo streams.
In Summary
It was a game changer for the usage of iPhones and iPads i.e., iOS 4. Apple similarly moved the iPhone from smartphone to mobile computing platform, bringing multitasking, folders, iBooks and iMessage support (over Wi-Fi with FaceTime), wireless printing and streaming to the formerly branded-with-an-iPhone-version-of-OS-X newly iOS-named device. This was the era of user comfort, cloudless media sharing, real freedom of choice in devices and it laid foundation for ever more developed updates to come over the next few years.
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