Android (operating system)

Android is a mobile operating system developed by Google, based on the Linux kernel and designed primarily for touchscreen mobile devices such as smartphones and tablets. Android's user interface is mainly based on direct manipulation, using touch gestures that loosely correspond to real-world actions, such as swiping, tapping and pinching, to manipulate on-screen objects, along with a virtual keyboard for text input. In addition to touchscreen devices, Google has further developed Android TV for televisions, Android Auto for cars, and Android Wear for wrist watches, each with a specialized user interface. Variants of Android are also used on game consoles, digital cameras, PCs and other electronics.

Initially developed by Android Inc., which Google bought in 2005, Android was unveiled in 2007, along with the founding of the Open Handset Alliance – a consortium of hardware, software, and telecommunication companies devoted to advancing open standards for mobile devices. Beginning with the first commercial Android device in September 2008, the operating system has gone through multiple major releases, with the current version being 8.0 "Oreo", released in August 2017. Android applications ("apps") can be downloaded from the Google Play store, which features over 2.7 million apps as of February 2017. Android has been the best-selling OS on tablets since 2013, and runs on the vast majority[a] of smartphones. As of May 2017, Android has two billion monthly active users, and it has the largest installed base of any operating system.

Android's source code is released by Google under an open source license, although most Android devices ultimately ship with a combination of free and open source and proprietary software, including proprietary software required for accessing Google services. Android is popular with technology companies that require a ready-made, low-cost and customizable operating system for high-tech devices. Its open nature has encouraged a large community of developers and enthusiasts to use the open-source code as a foundation for community-driven projects, which deliver updates to older devices, add new features for advanced users or bring Android to devices originally shipped with other operating systems. The extensive variation of hardware in Android devices causes significant delays for software upgrades, with new versions of the operating system and security patches typically taking months before reaching consumers, or sometimes not at all. The success of Android has made it a target for patent and copyright litigation between technology companies

Android Inc. was founded in Palo Alto, California in October 2003 by Andy Rubin, Rich Miner, Nick Sears, and Chris White.[12][13] Rubin described the Android project as "tremendous potential in developing smarter mobile devices that are more aware of its owner's location and preferences".[13] The early intentions of the company were to develop an advanced operating system for digital cameras, and this was the basis of its pitch to investors in April 2004.[14] The company then decided that the market for cameras was not large enough for its goals, and by five months later it had diverted its efforts and was pitching Android as a handset operating system that would rival Symbian and Microsoft Windows Mobile.[14][15]

Rubin had difficulty attracting investors early on, and Android was facing eviction from its office space. Steve Perlman, a close friend of Rubin, brought him $10,000 in cash in an envelope, and shortly thereafter wired an undisclosed amount as seed funding. Perlman refused a stake in the company, and has stated "I did it because I believed in the thing, and I wanted to help Andy."[16][17]

In July 2005,[13] Google acquired Android Inc. for at least $50 million.[18] Its key employees, including Rubin, Miner and White, joined Google as part of the acquisition.[13] Not much was known about the secretive Android at the time, with the company having provided few details other than that it was making software for mobile phones.[13] At Google, the team led by Rubin developed a mobile device platform powered by the Linux kernel. Google marketed the platform to handset makers and carriers on the promise of providing a flexible, upgradeable system.[19] Google had "lined up a series of hardware components and software partners and signaled to carriers that it was open to various degrees of cooperation".[20]

Speculation about Google's intention to enter the mobile communications market continued to build through December 2006.[21] An early prototype had a close resemblance to a BlackBerry phone, with no touchscreen and a physical QWERTY keyboard, but the arrival of 2007's Apple iPhone meant that Android "had to go back to the drawing board".[22][23] Google later changed its Android specification documents to state that "Touchscreens will be supported", although "the Product was designed with the presence of discrete physical buttons as an assumption, therefore a touchscreen cannot completely replace physical buttons".[24] In September 2007, InformationWeek covered an Evalueserve study reporting that Google had filed several patent applications in the area of mobile telephony.[25][26]
On November 5, 2007, the Open Handset Alliance, a consortium of technology companies including Google, device manufacturers such as HTC, Motorola and Samsung, wireless carriers such as Sprint and T-Mobile, and chipset makers such as Qualcomm and Texas Instruments, unveiled itself, with a goal to develop "the first truly open and comprehensive platform for mobile devices".[27][28][29] The first commercially available smartphone running Android was the HTC Dream, also known as T-Mobile G1, announced on September 23, 2008.[30][31]

Since 2008, Android has seen numerous updates which have incrementally improved the operating system, adding new features and fixing bugs in previous releases. Each major release is named in alphabetical order after a dessert or sugary treat, with the first few Android versions being called "Cupcake", "Donut", "Eclair", and "Froyo", respectively. During its announcement of Android KitKat in 2013, Google explained that "Since these devices make our lives so sweet, each Android version is named after a dessert", although a Google spokesperson told CNN in an interview that "It’s kind of like an internal team thing, and we prefer to be a little bit — how should I say — a bit inscrutable in the matter, I’ll say".[32]

In 2010, Google launched its Nexus series of devices, a lineup in which Google partnered with different device manufacturers to produce new devices and introduce new Android versions. The series was described as having "played a pivotal role in Android's history by introducing new software iterations and hardware standards across the board", and became known for its "bloat-free" software with "timely [...] updates".[33] At its developer conference in May 2013, Google announced a special version of the Samsung Galaxy S4, where, instead of using Samsung's own Android customization, the phone ran "stock Android" and was promised to receive new system updates fast.[34] The device would become the start of the Google Play edition program, and was followed by other devices, including the HTC One Google Play edition,[35] and Moto G Google Play edition.[36] In 2015, Ars Technica wrote that "Earlier this week, the last of the Google Play edition Android phones in Google's online storefront were listed as "no longer available for sale"" and that "Now they're all gone, and it looks a whole lot like the program has wrapped up".[37][38]

From 2008 to 2013, Hugo Barra served as product spokesperson, representing Android at press conferences and Google I/O, Google’s annual developer-focused conference. He left Google in August 2013 to join Chinese phone maker Xiaomi.[39][40] Less than six months earlier, Google's then-CEO Larry Page announced in a blog post that Andy Rubin had moved from the Android division to take on new projects at Google, and that Sundar Pichai would become the new Android lead.[41][42] Pichai himself would eventually switch positions, becoming the new CEO of Google in August 2015 following the company's restructure into the Alphabet conglomerate,[43][44] making Hiroshi Lockheimer the new head of Android.[45][46]

In June 2014, Google announced Android One, a set of "hardware reference models" that would "allow [device makers] to easily create high-quality phones at low costs", designed for consumers in developing countries.[47][48][49] In September, Google announced the first set of Android One phones for release in India.[50][51] However, Recode reported in June 2015 that the project was "a disappointment", citing "reluctant consumers and manufacturing partners" and "misfires from the search company that has never quite cracked hardware".[52] Plans to relaunch Android One surfaced in August 2015,[53] with Africa announced as the next location for the program a week later.[54][55] A report from The Information in January 2017 stated that Google is expanding its low-cost Android One program into the United States, although The Verge notes that the company will presumably not produce the actual devices itself.[56][57]

Google introduced the Pixel and Pixel XL smartphones in October 2016, marketed as being the first phones made by Google,[58][59] and exclusively featured certain software features, such as the Google Assistant, before wider rollout.[60][61] The Pixel phones replaced the Nexus series,[62] with a new generation of Pixel phones launched in October 2017.[63]
Interface
Android's default user interface is mainly based on direct manipulation, using touch inputs that loosely correspond to real-world actions, like swiping, tapping, pinching, and reverse pinching to manipulate on-screen objects, along with a virtual keyboard.[64] Game controllers and full-size physical keyboards are supported via Bluetooth or USB.[65][66] The response to user input is designed to be immediate and provides a fluid touch interface, often using the vibration capabilities of the device to provide haptic feedback to the user. Internal hardware, such as accelerometers, gyroscopes and proximity sensors are used by some applications to respond to additional user actions, for example adjusting the screen from portrait to landscape depending on how the device is oriented,[67] or allowing the user to steer a vehicle in a racing game by rotating the device, simulating control of a steering wheel.[68]

Android devices boot to the homescreen, the primary navigation and information "hub" on Android devices, analogous to the desktop found on personal computers. Android homescreens are typically made up of app icons and widgets; app icons launch the associated app, whereas widgets display live, auto-updating content, such as a weather forecast, the user's email inbox, or a news ticker directly on the homescreen.[69] A homescreen may be made up of several pages, between which the user can swipe back and forth.[70] Third-party apps available on Google Play and other app stores can extensively re-theme the homescreen,[71] and even mimic the look of other operating systems, such as Windows Phone.[72] Most manufacturers customize the look and features of their Android devices to differentiate themselves from their competitors.[73]

Along the top of the screen is a status bar, showing information about the device and its connectivity. This status bar can be "pulled" down to reveal a notification screen where apps display important information or updates.[70] Notifications are "short, timely, and relevant information about your app when it’s not in use", and when tapped, users are directed to a screen inside the app relating to the notification.[74] Beginning with Android 4.1 "Jelly Bean", "expandable notifications" allow the user to tap an icon on the notification in order for it to expand and display more information and possible app actions right from the notification.[75]

An All Apps screen lists all installed applications, with the ability for users to drag an app from the list onto the home screen. A Recents screen lets users switch between recently used apps.[70]

Applications
See also: Android software development and Google Play
Applications ("apps"), which extend the functionality of devices, are written using the Android software development kit (SDK)[76] and, often, the Java programming language.[77] Java may be combined with C/C++,[78] together with a choice of non-default runtimes that allow better C++ support.[79] The Go programming language is also supported, although with a limited set of application programming interfaces (API).[80] In May 2017, Google announced support for Android app development in the Kotlin programming language.[81][82]

The SDK includes a comprehensive set of development tools,[83] including a debugger, software libraries, a handset emulator based on QEMU, documentation, sample code, and tutorials. Initially, Google's supported integrated development environment (IDE) was Eclipse using the Android Development Tools (ADT) plugin; in December 2014, Google released Android Studio, based on IntelliJ IDEA, as its primary IDE for Android application development. Other development tools are available, including a native development kit (NDK) for applications or extensions in C or C++, Google App Inventor, a visual environment for novice programmers, and various cross platform mobile web applications frameworks. In January 2014, Google unveiled an framework based on Apache Cordova for porting Chrome HTML 5 web applications to Android, wrapped in a native application shell.[84]

Android has a growing selection of third-party applications, which can be acquired by users by downloading and installing the application's APK (Android application package) file, or by downloading them using an application store program that allows users to install, update, and remove applications from their devices. Google Play Store is the primary application store installed on Android devices that comply with Google's compatibility requirements and license the Google Mobile Services software.[85][86] Google Play Store allows users to browse, download and update applications published by Google and third-party developers; as of July 2013, there are more than one million applications available for Android in Play Store.[87] As of July 2013, 50 billion applications have been installed.[88][89] Some carriers offer direct carrier billing for Google Play application purchases, where the cost of the application is added to the user's monthly bill.[90] As of May 2017, there are over one billion active users a month for Gmail, Android, Chrome, Google Play and Maps.

Due to the open nature of Android, a number of third-party application marketplaces also exist for Android, either to provide a substitute for devices that are not allowed to ship with Google Play Store, provide applications that cannot be offered on Google Play Store due to policy violations, or for other reasons. Examples of these third-party stores have included the Amazon Appstore, GetJar, and SlideMe. F-Droid, another alternative marketplace, seeks to only provide applications that are distributed under free and open source licenses.[85][91][92][93]

Memory management
Since Android devices are usually battery-powered, Android is designed to manage processes to keep power consumption at a minimum. When an application is not in use the system suspends its operation so that, while available for immediate use rather than closed, it does not use battery power or CPU resources.[94][95] Android manages the applications stored in memory automatically: when memory is low, the system will begin invisibly and automatically closing inactive processes, starting with those that have been inactive for longest.[96][97] Lifehacker reported in 2011 that third-party task killers were doing more harm than good.[98]

Virtual reality
At Google I/O on May 2016, Google announced Daydream, a virtual reality platform that relies on a smartphone and provides VR capabilities through a virtual reality headset and controller designed by Google itself.[99] The platform is built into Android starting with Android Nougat, differentiating from standalone support for VR capabilities. The software is available for developers, and was released in 2016.

Hardware

The main hardware platform for Android is the ARM (ARMv7 and ARMv8-A architectures), with x86, MIPS and MIPS64, and x86-64 architectures also officially supported in later versions of Android.[100][101][102] The unofficial Android-x86 project provided support for the x86 architectures ahead of the official support.[103][104] MIPS architecture was also supported before Google did. Since 2012, Android devices with Intel processors began to appear, including phones[105] and tablets. While gaining support for 64-bit platforms, Android was first made to run on 64-bit x86 and then on ARM64. Since Android 5.0 "Lollipop", 64-bit variants of all platforms are supported in addition to the 32-bit variants.[100]

Requirements for the minimum amount of RAM for devices running Android 7.1 range from in practice 2 GB for best hardware, down to 1 GB for the most common screen, to absolute minimum 512 MB for lowest spec 32-bit smartphone. The recommendation for Android 4.4 is to have at least 512 MB of RAM,[106] while for "low RAM" devices 340 MB is the required minimum amount that does not include memory dedicated to various hardware components such as the baseband processor.[107] Android 4.4 requires a 32-bit ARMv7, MIPS or x86 architecture processor (latter two through unofficial ports),[103][108] together with an OpenGL ES 2.0 compatible graphics processing unit (GPU).[109] Android supports OpenGL ES 1.1, 2.0, 3.0, 3.1 and as of latest major version, 3.2 and Vulkan. Some applications may explicitly require a certain version of the OpenGL ES, and suitable GPU hardware is required to run such applications.[109]

Android devices incorporate many optional hardware components, including still or video cameras, GPS, orientation sensors, dedicated gaming controls, accelerometers, gyroscopes, barometers, magnetometers, proximity sensors, pressure sensors, thermometers, and touchscreens. Some hardware components are not required, but became standard in certain classes of devices, such as smartphones, and additional requirements apply if they are present. Some other hardware was initially required, but those requirements have been relaxed or eliminated altogether. For example, as Android was developed initially as a phone OS, hardware such as microphones were required, while over time the phone function became optional.[89] Android used to require an autofocus camera, which was relaxed to a fixed-focus camera[89] if present at all, since the camera was dropped as a requirement entirely when Android started to be used on set-top boxes.

In addition to running on smartphones and tablets, several vendors run Android natively on regular PC hardware with a keyboard and mouse.[110][111][112][113] In addition to their availability on commercially available hardware, similar PC hardware-friendly versions of Android are freely available from the Android-x86 project, including customized Android 4.4.[114] Using the Android emulator that is part of the Android SDK, or third-party emulators, Android can also run non-natively on x86 architectures.[115][116] Chinese companies are building a PC and mobile operating system, based on Android, to "compete directly with Microsoft Windows and Google Android".[117] The Chinese Academy of Engineering noted that "more than a dozen" companies were customising Android following a Chinese ban on the use of Windows 8 on government PCs.[118][119][120]

Development
Android is developed by Google until the latest changes and updates are ready to be released, at which point the source code is made available to the Android Open Source Project.[121] This source code can be found without modification on select devices, mainly the Nexus series of devices.[122] The source code is, in turn, adapted by original equipment manufacturers (OEMs) to run on their hardware.[123][124] Android's source code does not contain the often proprietary device drivers that are needed for certain hardware components.[125]

In 2007, the green Android logo was designed for Google by graphic designer Irina Blok. The design team was tasked with a project to create a universally identifiable icon with the specific inclusion of a robot in the final design. After numerous design developments based on science fiction and space movies, the team eventually sought inspiration from the human symbol on restroom doors and modified the figure into a robot shape. As Android is open-source, it was agreed that the logo should be likewise, and since its launch the green logo has been reinterpreted into countless variations on the original design.[126]
Update schedule
Google announces major incremental upgrades to Android on a yearly basis.[127] The updates can be installed on devices over-the-air.[128] The latest major release is 8.0 "Oreo", announced in March 2017,[129] and released the following August.[130][131]

Compared to its primary rival mobile operating system, Apple's iOS, Android updates typically reach various devices with significant delays. Except for devices within the Google Nexus brand, updates often arrive months after the release of the new version, or not at all.[132] This is partly due to the extensive variation in hardware in Android devices,[133] to which each upgrade must be specifically tailored, a time- and resource-consuming process.[134] Manufacturers often prioritize their newest devices and leave old ones behind.[135] Additional delays can be introduced by wireless carriers that, after receiving updates from manufacturers, further customize and brand Android to their needs and conduct extensive testing on their networks before sending the upgrade out to users.[135][136] There are also situations in which upgrades are not possible due to one manufacturing partner not providing necessary updates to drivers.[137]

The lack of after-sale support from manufacturers and carriers has been widely criticized by consumer groups and the technology media.[138][139][140] Some commentators have noted that the industry has a financial incentive not to upgrade their devices, as the lack of updates for existing devices fuels the purchase of newer ones,[141] an attitude described as "insulting".[140] The Guardian complained that the method of distribution for updates is complicated only because manufacturers and carriers have designed it that way.[140] In 2011, Google partnered with a number of industry players to announce an "Android Update Alliance", pledging to deliver timely updates for every device for 18 months after its release; however, there has not been another official word about that alliance since its announcement.[135][142]

In 2012, Google began decoupling certain aspects of the operating system (particularly its core applications) so they could be updated through the Google Play store independently of the OS. One of those components, Google Play Services, is a closed-source system-level process providing APIs for Google services, installed automatically on nearly all devices running Android 2.2 "Froyo" and higher. With these changes, Google can add new system functionality through Play Services and update apps without having to distribute an upgrade to the operating system itself.[143] As a result, Android 4.2 and 4.3 "Jelly Bean" contained relatively fewer user-facing changes, focusing more on minor changes and platform improvements.[144]

In May 2016, Bloomberg reported that Google was making efforts to keep Android more up-to-date, including accelerated rates of security updates, rolling out technological workarounds, reducing requirements for phone testing, and ranking phone makers in an attempt to "shame" them into better behavior. As stated by Bloomberg: "As smartphones get more capable, complex and hackable, having the latest software work closely with the hardware is increasingly important". Hiroshi Lockheimer, the Android lead, admitted that "It’s not an ideal situation", further commenting that the lack of updates is "the weakest link on security on Android". Wireless carriers were described in the report as the "most challenging discussions", due to carriers' slow approval time due to testing on their networks, despite some carriers, including Verizon and Sprint, having already shortened their respective approval times. HTC's then-executive Jason Mackenzie called monthly security updates "unrealistic" in 2015, and Google was trying to persuade carriers to exclude security patches from the full testing procedures. In a further effort for persuasion, Google shared a list of top phone makers measured by updated devices with its Android partners, and is considering making the list public. Mike Chan, co-founder of phone maker Nextbit and former Android developer, said that "The best way to solve this problem is a massive re-architecture of the operating system", "or Google could invest in training manufacturers and carriers "to be good Android citizens"".[145][146][147]

In May 2017, with the announcement of Android 8.0, Google introduced Project Treble, a major re-architect of the Android OS framework designed to make it easier, faster, and less costly for manufacturers to update devices to newer versions of Android. Project Treble separates the vendor implementation (device-specific, lower-level software written by silicon manufacturers) from the Android OS framework via a new "vendor interface". In Android 7.0 and earlier, no formal vendor interface exists, so device makers must update large portions of the Android code to move a device to a newer version of the operating system. With Treble, the new stable vendor interface provides access to the hardware-specific parts of Android, enabling device makers to deliver new Android releases simply by updating the Android OS framework, "without any additional work required from the silicon manufacturers."[148]

In September 2017, Google's Project Treble team revealed that, as part of their efforts to improve the security lifecycle of Android devices, Google had managed to get the Linux Foundation to agree to extend the support lifecycle of the Linux Long-Term Support (LTS) kernel branch from the 2 years that it has historically lasted to 6 years for future versions of the LTS kernel, starting with Linux kernel 4.4.[149]

Linux kernel
Android's kernel is based on one of the Linux kernel's long-term support (LTS) branches. As of 2017, Android devices mainly use versions 3.18 or 4.4 of the Linux kernel.[150] The actual kernel depends on the individual device.[151]

Android's variant of the Linux kernel has further architectural changes that are implemented by Google outside the typical Linux kernel development cycle, such as the inclusion of components like device trees, ashmem, ION, and different Out of memory (OOM) handling.[152][153] Certain features that Google contributed back to the Linux kernel, notably a power management feature called "wakelocks",[154] were initially rejected by mainline kernel developers partly because they felt that Google did not show any intent to maintain its own code.[155][156] Google announced in April 2010 that they would hire two employees to work with the Linux kernel community,[157] but Greg Kroah-Hartman, the current Linux kernel maintainer for the stable branch, said in December 2010 that he was concerned that Google was no longer trying to get their code changes included in mainstream Linux.[156] Google engineer Patrick Brady once stated in the company's developer conference that "Android is not Linux",[158] with Computerworld adding that "Let me make it simple for you, without Linux, there is no Android".[159] Ars Technica wrote that "Although Android is built on top of the Linux kernel, the platform has very little in common with the conventional desktop Linux stack".[158]

In August 2011, Linus Torvalds said that "eventually Android and Linux would come back to a common kernel, but it will probably not be for four to five years".[160] In December 2011, Greg Kroah-Hartman announced the start of Android Mainlining Project, which aims to put some Android drivers, patches and features back into the Linux kernel, starting in Linux 3.3.[161] Linux included the autosleep and wakelocks capabilities in the 3.5 kernel, after many previous attempts at merger. The interfaces are the same but the upstream Linux implementation allows for two different suspend modes: to memory (the traditional suspend that Android uses), and to disk (hibernate, as it is known on the desktop).[162] Google maintains a public code repository that contains their experimental work to re-base Android off the latest stable Linux versions.[163][164]

The flash storage on Android devices is split into several partitions, such as /system for the operating system itself, and /data for user data and application installations.[165] In contrast to desktop Linux distributions, Android device owners are not given root access to the operating system and sensitive partitions such as /system are read-only. However, root access can be obtained by exploiting security flaws in Android, which is used frequently by the open-source community to enhance the capabilities of their devices,[166] but also by malicious parties to install viruses and malware.[167]

Android is a Linux distribution according to the Linux Foundation,[168] Google's open-source chief Chris DiBona,[169] and several journalists.[170][171] Others, such as Google engineer Patrick Brady, say that Android is not Linux in the traditional Unix-like Linux distribution sense; Android does not include the GNU C Library (it uses Bionic as an alternative C library) and some of other components typically found in Linux distributions.[172]

As of latest version, Android Oreo, Google "mandates a minimum kernel version and kernel configuration" for security reasons, e.g. Linux kernel 4.4 or newer (version number requirement can be relaxed based on hardware, or dropped for upgraded devices).[173]