Google Earth Pro - 2007 Version serial key or number

Commercial logo as used by Google, since 2019
Android 11 home screen with Pixel Launcher
Developer	Various (mostly Google and the Open Handset Alliance)
Written in	Java (UI), C (core), C++ and others[1]
OS family	Unix-like (Modified Linux kernel)
Working state	Current
Source model	Open source (most devices include proprietary components, such as Google Play)
Initial release	September 23, 2008; 12 years ago (2008-09-23)[2]
Latest release	Android 11 / September 8, 2020; 16 days ago (2020-09-08)[3]
Repository
Marketing target	Smartphones, tablet computers, smart TVs (Android TV), Android Auto and smartwatches (Wear OS)
Available in	100+ languages[4]
Update method	Over-the-air
Package manager	APK-based
Platforms	64-bit (32-bit being dropped) ARM, x86 and x86-64
Kernel type	Linux kernel
Userland	Bionic libc,[5]mksh shell,[6]Toybox as core utilities (beginning with Android 6.0)[7][8]
Default user interface	Graphical (multi-touch)
License
Official website	www.android.com
Articles in the series
Android version history

Android is a mobile operating system based on a modified version of the Linux kernel and other open source software, designed primarily for touchscreen mobile devices such as smartphones and tablets. Android is developed by a consortium of developers known as the Open Handset Alliance and commercially sponsored by Google. It was unveiled in November 2007, with the first commercial Android device launched in September 2008.

It is free and open source software; its source code is known as Android Open Source Project (AOSP), which is primarily licensed under the Apache License. However most Android devices ship with additional proprietary software pre-installed,^[10] most notably Google Mobile Services (GMS)^[11] which includes core apps such as Google Chrome, the digital distribution platform Google Play and associated Google Play Services development platform. About 70 percent of Android smartphones run Google's ecosystem;^[12] competing Android ecosystems and forks include Fire OS (developed by Amazon) or LineageOS. However the "Android" name and logo are trademarks of Google which impose standards to restrict "uncertified" devices outside their ecosystem to use Android branding.^[13][14]

The source code has been used to develop variants of Android on a range of other electronics, such as game consoles, digital cameras, portable media players, PCs and others, each with a specialized user interface. Some well known derivatives include Android TV for televisions and Wear OS for wearables, both developed by Google. Software packages on Android, which use the APK format, are generally distributed through proprietary application stores like Google Play Store, Samsung Galaxy Store, and Huawei AppGallery, or open source platforms like Aptoide or F-Droid.

Android has been the best-selling OS worldwide on smartphones since 2011 and on tablets since 2013. As of May 2017^[update], it has over two billion monthly active users, the largest installed base of any operating system, and as of August 2020^[update], the Google Play Store features over 3 million apps.^[15] The current stable version is Android 11, released on September 8, 2020.

History

First Android logotype (2007–2014)

Second Android logotype (2014–2019)

Third Android logotype (2019–present)

Android Inc. was founded in Palo Alto, California, in October 2003 by Andy Rubin, Rich Miner, Nick Sears, and Chris White.^[16][17] Rubin described the Android project as "tremendous potential in developing smarter mobile devices that are more aware of its owner's location and preferences".^[17] 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.^[18] 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.^[18][19]

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."^[20][21]

In July 2005,^[17]Google acquired Android Inc. for at least $50 million.^[22] Its key employees, including Rubin, Miner and White, joined Google as part of the acquisition.^[17] 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.^[17] 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.^[23] 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".^{[attribution needed][24]}

Speculation about Google's intention to enter the mobile communications market continued to build through December 2006.^[25] An early prototype had a close resemblance to a BlackBerry phone, with no touchscreen and a physical QWERTYkeyboard, but the arrival of 2007's AppleiPhone meant that Android "had to go back to the drawing board".^[26][27] 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".^[28] By 2008, both Nokia and BlackBerry announced touch-based smartphones to rival the iPhone 3G, and Android's focus eventually switched to just touchscreens. The first commercially available smartphone running Android was the HTC Dream, also known as T-Mobile G1, announced on September 23, 2008.^[29][30]

HTC Dream or T-Mobile G1, the first commercially released device running Android (2008)

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".^[31][32][33] Within a year, the Open Handset Alliance faced two other open source competitors, the Symbian Foundation and the LiMo Foundation, the latter also developing a Linux-based mobile operating system like Google. In September 2007, InformationWeek covered an Evalueserve study reporting that Google had filed several patent applications in the area of mobile telephony.^[34][35]

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", in that order. 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".^[36]

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".^[37] 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.^[38] 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,^[39] and Moto G Google Play edition.^[40] 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".^[41][42]

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.^[43][44] Less than six months earlier, Google's then-CEOLarry 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.^[45][46] Pichai himself would eventually switch positions, becoming the new CEO of Google in August 2015 following the company's restructure into the Alphabet conglomerate,^[47][48] making Hiroshi Lockheimer the new head of Android.^[49][50]

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.^[51][52][53] In September, Google announced the first set of Android One phones for release in India.^[54][55] 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".^[56] Plans to relaunch Android One surfaced in August 2015,^[57] with Africa announced as the next location for the program a week later.^[58][59] 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.^[60][61]

Google introduced the Pixel and Pixel XL smartphones in October 2016, marketed as being the first phones made by Google,^[62][63] and exclusively featured certain software features, such as the Google Assistant, before wider rollout.^[64][65] The Pixel phones replaced the Nexus series,^[66] with a new generation of Pixel phones launched in October 2017.^[67]

In May 2019, the operating system became entangled in the trade war between China and the United States involving Huawei which like many other tech firms have become dependent on access to the Android platform.^[68][69] In the summer of 2019, Huawei announced it would create an alternative operating system to Android^[70][71] known as Harmony OS,^[72] and have filed for intellectual property rights across major global markets.^[73][74] Huawei does not currently have any plans to replace Android in the near future, as Harmony OS is designed for internet of things devices, rather than for smartphones.^[75]

On August 22, 2019, it was announced that Android "Q" would officially be branded as Android 10, ending the historic practice of naming major versions after desserts. Google stated that these names were not "inclusive" to international users (due either to the aforementioned foods not being internationally known, or being difficult to pronounce in some languages).^[76][77] On the same day, Android Police reported that Google had commissioned a statue of a giant number "10" to be installed in the lobby of the developers' new office.^[78] Android 10 was released on September 3, 2019 to Google Pixel phones first.

Features

Interface

English: Android 10 home screen on Motorola G7

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.^[79]Game controllers and full-size physical keyboards are supported via Bluetooth or USB.^[80][81] 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,^[82] or allowing the user to steer a vehicle in a racing game by rotating the device, simulating control of a steering wheel.^[83]

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.^[84] A homescreen may be made up of several pages, between which the user can swipe back and forth.^[85] Third-party apps available on Google Play and other app stores can extensively re-theme the homescreen,^[86] and even mimic the look of other operating systems, such as Windows Phone.^[87] Most manufacturers customize the look and features of their Android devices to differentiate themselves from their competitors.^[88]

English: all sorts of Android widgets. email/message, app shortcut, music miniplayer , search bar and information bar

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.^[85] 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.^[89] 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.^[90]

Notification tray displaying both active and silent notifications

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.^[85]

Recent apps on Android 10 (Motorola g7). apps are Wikimedia commons and Wikipedia

Applications

Many, to almost all, Android devices come with preinstalled Google apps including Gmail, Google Maps, Google Chrome, YouTube, Google Play Music, Google Play Movies & TV, and many more.

Applications ("apps"), which extend the functionality of devices (and must be 64-bit^[91]), are written using the Android software development kit (SDK)^[92] and, often, Kotlin programming language, which replaced Java as Google's preferred language for Android app development in May 2019,^[93] and was originally announced in May 2017.^[94][95] Java is still supported (originally the only option for user-space programs, and is often mixed with Kotlin), as is C++.^[96] Java and/or other JVM languages, such as Kotlin, may be combined with C/C++,^[97] together with a choice of non-default runtimes that allow better C++ support.^[98] The Go programming language is also supported, although with a limited set of application programming interfaces (API).^[99]

The SDK includes a comprehensive set of development tools,^[100] 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 a framework based on Apache Cordova for porting ChromeHTML 5web applications to Android, wrapped in a native application shell.^[101] Additionally, Firebase was acquired by Google in 2014 that provides helpful tools for app and web developers.^[102][103]

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.^[104][105] Google Play Store allows users to browse, download and update applications published by Google and third-party developers; as of August 2020^[update], there are more than three million applications available for Android in Play Store.^[15][106] As of July 2013^[update], 50 billion applications have been installed.^[107][108] 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.^[109] As of May 2017^[update], 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 sourcelicenses.^{[104][110][111][112]}

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.^[113][114] 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 the longest amount of time.^[115][116] Lifehacker reported in 2011 that third-party task killer applications were doing more harm than good.^[117]

Hardware

The main hardware platform for Android is ARM (the ARMv7 and ARMv8-A architectures), with x86 and x86-64 architectures also officially supported in later versions of Android.^{[118][119][120][121]} The unofficial Android-x86 project provided support for x86 architectures ahead of the official support.^[122][123] The ARMv5TE and MIPS32/64 architectures were also historically supported but removed in later Android releases.^[124] Since 2012, Android devices with Intel processors began to appear, including phones^[125] 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.^[118]

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 the lowest spec 32-bit smartphone. The recommendation for Android 4.4 is to have at least 512 MB of RAM,^[126] 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.^[127] Android 4.4 requires a 32-bitARMv7, MIPS or x86 architecture processor (latter two through unofficial ports),^[122][123] together with an OpenGL ES 2.0 compatible graphics processing unit (GPU).^[128] Android supports OpenGL ES 1.1, 2.0, 3.0, 3.1 and 3.2 and since Android 7.0 Vulkan (and version 1.1 available for some devices^[129]). Some applications may explicitly require a certain version of the OpenGL ES, and suitable GPU hardware is required to run such applications.^[128]

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.^[108] Android used to require an autofocus camera, which was relaxed to a fixed-focus camera^[108] 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.^{[130][131][132][133]} 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.^[134] Using the Android emulator that is part of the Android SDK, or third-party emulators, Android can also run non-natively on x86 architectures.^[135][136] Chinese companies are building a PC and mobile operating system, based on Android, to "compete directly with Microsoft Windows and Google Android".^[137] 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.^{[138][139][140]}

Development

The stack of Android Open Source Project

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 (AOSP),^[141] an open source initiative led by Google.^[142] The AOSP code can be found without modification on select devices, mainly the former Nexus and current Android One series of devices.^[143]

The source code is, in turn, customized by original equipment manufacturers (OEMs) to run on their hardware.^[144][145] Android's source code does not contain the device drivers, often proprietary, that are needed for certain hardware components.^[146] As a result, most Android devices, including Google's own, ship with a combination of free and open source and proprietary software, with the software required for accessing Google services falling into the latter category.

Update schedule

Google announces major incremental upgrades to Android on a yearly basis.^[147] The updates can be installed on devices over-the-air.^[148] The latest major release is Android 10.

The extensive variation of hardware^[149] in Android devices has caused significant delays for software upgrades and security patches. Each upgrade has had to be specifically tailored, a time- and resource-consuming process.^[150] Except for devices within the Google Nexus and Pixel brands, updates have often arrived months after the release of the new version, or not at all.^[151] Manufacturers often prioritize their newest devices and leave old ones behind.^[152] Additional delays can be introduced by wireless carriers who, after receiving updates from manufacturers, further customize Android to their needs and conduct extensive testing on their networks before sending out the upgrade.^[152][153] There are also situations in which upgrades are impossible due to a manufacturer not updating necessary drivers.^[154]

The lack of after-sale support from manufacturers and carriers has been widely criticized by consumer groups and the technology media.^{[155][156][157]} 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,^[158] an attitude described as "insulting".^[157]The Guardian complained that the method of distribution for updates is complicated only because manufacturers and carriers have designed it that way.^[157] 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.^[152][159]

In 2012, Google began de-coupling certain aspects of the operating system (particularly its central 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 functions and update apps without having to distribute an upgrade to the operating system itself.^[160] 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.^[161]

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 May 2016, Bloomberg Businessweek 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 their slow approval time while testing on their networks, despite some carriers, including Verizon Wireless and Sprint Corporation, already shortening their approval times. 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.^[when?] 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'".^{[162][163][164]}

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."^[165]

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.^[166]

In May 2019, with the announcement of Android 10, Google introduced Project Mainline to simplify and expedite delivery of updates to the Android ecosystem. Project Mainline enables updates to core OS components through the Google Play Store. As a result, important security and performance improvements that previously needed to be part of full OS updates can be downloaded and installed as easily as an app update.^[167]

Linux kernel

Android's kernel is based on the Linux kernel's long-term support (LTS) branches. As of 2020^[update], Android uses versions 4.4, 4.9 or 4.14 of the Linux kernel.^[168] The actual kernel depends on the individual device.^[169]

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.^[170][171] Certain features that Google contributed back to the Linux kernel, notably a power management feature called "wakelocks",^[172] were initially rejected by mainline kernel developers partly because they felt that Google did not show any intent to maintain its own code.^[173][174] Google announced in April 2010 that they would hire two employees to work with the Linux kernel community,^[175] 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.^[174] Google engineer Patrick Brady once stated in the company's developer conference that "Android is not Linux",^[176] with Computerworld adding that "Let me make it simple for you, without Linux, there is no Android".^[177]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".^[176]

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".^[178] 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.^[179] 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).^[180] Google maintains a public code repository that contains their experimental work to re-base Android off the latest stable Linux versions.^[181][182]

The flash storage on Android devices is split into several partitions, such as for the operating system itself, and for user data and application installations.^[183] 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, but also by malicious parties to install viruses and malware.^[184]

Android is a Linux distribution according to the Linux Foundation,^[185] Google's open-source chief Chris DiBona,^[186] and several journalists.^[187][188] 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.^[189]

With the release of Android Oreo in 2017, Google began to require that devices shipped with new SoCs had Linux kernel version 4.4 or newer, for security reasons. Existing devices upgraded to Oreo, and new products launched with older SoCs, were exempt from this rule.^[190][191]

Software stack

Android's architecture diagram

On top of the Linux kernel, there are the middleware, libraries and APIs written in C, and application software running on an application framework which includes Java-compatible libraries. Development of the Linux kernel continues independently of Android's other source code projects.

Android uses Android Runtime (ART) as its runtime environment (introduced in version 4.4), which uses ahead-of-time (AOT) compilation to entirely compile the application bytecode into machine code upon the installation of an application. In Android 4.4, ART was an experimental feature and not enabled by default; it became the only runtime option in the next major version of Android, 5.0.^[192] In versions no longer supported, until version 5.0 when ART took over, Android previously used Dalvik as a process virtual machine with trace-based just-in-time (JIT) compilation to run Dalvik "dex-code" (Dalvik Executable), which is usually translated from the Java bytecode. Following the trace-based JIT principle, in addition to interpreting the majority of application code, Dalvik performs the compilation and native execution of select frequently executed code segments ("traces") each time an application is launched.^{[193][194][195]} For its Java library, the Android platform uses a subset of the now discontinued Apache Harmony project.^[196] In December 2015, Google announced that the next version of Android would switch to a Java implementation based on the OpenJDK project.^[197]

Android's standard C library, Bionic, was developed by Google specifically for Android, as a derivation of the BSD's standard C library code. Bionic itself has been designed with several major features specific to the Linux kernel. The main benefits of using Bionic instead of the GNU C Library (glibc) or uClibc are its smaller runtime footprint, and optimization for low-frequency CPUs. At the same time, Bionic is licensed under the terms of the BSD licence, which Google finds more suitable for the Android's overall licensing model.^[195]

Aiming for a different licensing model, toward the end of 2012, Google switched the Bluetooth stack in Android from the GPL-licensed BlueZ to the Apache-licensed BlueDroid.^[198]

Android does not have a native X Window System by default, nor does it support the full set of standard GNU libraries. This made it difficult to port existing Linux applications or libraries to Android,^[189] until version r5 of the Android Native Development Kit brought support for applications written completely in C or C++.^[199] Libraries written in C may also be used in applications by injection of a small shim and usage of the JNI.^[200]

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