Android (operating system)


Android (operating system)

Android is a mobile operating system (OS) currently 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 notebooksgame consolesdigital cameras, and other electronics.
Android has the largest installed base of all operating systems of any kind. Android has been the best selling OS on tablets since 2013, and on smartphones it is dominant by any metric.[14][15]
Initially developed by Android, Inc., which Google bought in 2005,[16] Android was unveiled in 2007, along with the founding of the Open Handset Alliance – a consortium of hardwaresoftware, and telecommunication companies devoted to advancing open standards for mobile devices.[17] As of July 2013, the Google Play store has had over one million Android applications ("apps") published, and over 50 billion applications downloaded.[18] An April–May 2013 survey of mobile application developers found that 71% of developers create applications for Android,[19] and a 2015 survey found that 40% of full-time professional developers see Android as their priority target platform, which is comparable to Apple's iOS on 37% with both platforms far above others.[20] At Google I/O 2014, the company revealed that there were over one billion active monthly Android users, up from 538 million in June 2013.[21]

Android's source code is released by Google under open source licenses, although most Android devices ultimately ship with a combination of open source and proprietary software, including proprietary software required for accessing Google services.[3] Android is popular with technology companies that require a ready-made, low-cost and customizable operating system for high-tech devices.[22] 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 add new features for advanced users[23] or bring Android to devices originally shipped with other operating systems. At the same time, as Android has no centralised update system most Android devices fail to receive security updates: research in 2015 concluded that almost 90% of Android phones in use had known but unpatched security vulnerabilities due to lack of updates and support.[24][25] The success of Android has made it a target for patent litigation as part of the so-called "smartphone wars" between technology companies.[26][27]

History of android operating system

Android, Inc. was founded in Palo Alto, California in October 2003 by Andy Rubin (co-founder of Danger),[28] Rich Miner (co-founder of Wildfire Communications, Inc.),[29] Nick Sears (once VP at T-Mobile),[30] and Chris White (headed design and interface development at WebTV[16]) to develop, in Rubin's words, "smarter mobile devices that are more aware of its owner's location and preferences".[16] The early intentions of the company were to develop an advanced operating system for digital cameras. Though, when it was realized that the market for the devices was not large enough, the company diverted its efforts toward producing a smartphone operating system that would rival Symbian and Microsoft Windows Mobile.[31] Despite the past accomplishments of the founders and early employees, Android Inc. operated secretly, revealing only that it was working on software for mobile phones.[16] That same year, Rubin ran out of money. Steve Perlman, a close friend of Rubin, brought him $10,000 in cash in an envelope and refused a stake in the company.[32]
In July 2005, Google acquired Android Inc. for at least $50 million, whose key employees, including Rubin, Miner and White, stayed at the company after the acquisition.[14][16] Not much was known about Android Inc. at the time, but many assumed that Google was planning to enter the mobile phone market with this move.[16] 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, upgradable system. Google had lined up a series of hardware component and software partners and signaled to carriers that it was open to various degrees of cooperation on their part.[33][34][35]
Speculation about Google's intention to enter the mobile communications market continued to build through December 2006.[36] An earlier prototype codenamed "Sooner" had a closer resemblance to a BlackBerry phone, with no touchscreen, and a physical, QWERTY keyboard, but was later re-engineered to support a touchscreen, to compete with other announced devices such as the 2006 LG Prada and 2007 Apple iPhone.[37][38] In September 2007, InformationWeek covered an Evalueserve study reporting that Google had filed several patent applications in the area of mobile telephony.[39][40]
Eric SchmidtAndy Rubin and Hugo Barra at a 2012 press conference announcing Google's Nexus 7 tablet
On November 5, 2007, the Open Handset Alliance, a consortium of technology companies including Google, device manufacturers such as HTCSony and Samsung, wireless carriers such as Sprint Nextel and T-Mobile, and chipset makers such as Qualcomm and Texas Instruments, unveiled itself, with a goal to develop open standards for mobile devices.[17] That day, Android was unveiled as its first product, a mobile device platform built on the Linux kernel.[17][41] The first commercially available smartphone running Android was theHTC Dream, released on October 22, 2008.[42]
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; for example, version 1.5 "Cupcake" was followed by 1.6 "Donut". In 2010, Google launched its Nexus series of devices – a line of smartphones and tablets running the Android operating system, and built by manufacturing partners. HTC collaborated with Google to release the first Nexus smartphone,[43] the Nexus One. Google has since updated the series with newer devices, such as the Nexus 5 phone (made by LG) and the Nexus 7 tablet (made by Asus). Google releases the Nexus phones and tablets to act as their flagship Android devices, demonstrating Android's latest software and hardware features. From 2013 until 2015, Google offered several Google Play Edition devices over Google Play. While not carrying the Google Nexus branding, these were Google-customized Android phones and tablets that also ran the latest version of Android, free from manufacturer or carrier modifications.
From 2010 to 2013, Hugo Barra served as product spokesperson, representing Android at press conferences and Google I/O, Google’s annual developer-focused conference. Barra's product involvement included the entire Android ecosystem of software and hardware, including Honeycomb, Ice Cream Sandwich, Jelly Bean and KitKat operating system launches, the Nexus 4 and Nexus 5 smartphones, the Nexus 7[44] and Nexus 10 tablets,[45] and other related products such as Google Now[46] and Google Voice Search, Google’s speech recognition product comparable to Apple’s Siri.[46] In 2013, Barra left the Android team for Chinese smartphone maker Xiaomi.[47] The same year, Larry Pageannounced in a blog post that Andy Rubin had moved from the Android division to take on new projects at Google.[48] He was replaced by Sundar Pichai who became the new head of Android and Chrome OS,[49] and, later, by Hiroshi Lockheimer when Pichai became CEO of Google.[50]
In 2014, Google launched Android One, a line of smartphones mainly targeting customers in the developing world. In May 2015, Google announced Project Brillo as a cut-down version of Android that uses its lower levels (excluding the user interface), intended for the "Internet of Things" (IoT) embedded systems.[51]


Software stack & Open-source community of android operating system

On top of the Linux kernel, there are the middlewarelibraries 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 other Android's source code bases.
Until version 5.0, Android 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 andnative execution of select frequently executed code segments ("traces") each time an application is launched.[138][139][140] Android 4.4 introduced Android Runtime (ART) as a new runtime environment, which usesahead-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.[141]
For its Java library, the Android platform uses a subset of the now discontinued Apache Harmony project.[142] In December 2015, Google announced that the next version of Android would switch to a Java implementation based onOpenJDK.[143]
Android's standard C libraryBionic, 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.[140]
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.[144]
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,[137] until version r5 of the Android Native Development Kit brought support for applications written completely in C or C++.[145] Libraries written in C may also be used in applications by injection of a small shim and usage of the JNI.[146]
Since Marshmallow, "Toybox", a collection of command line utilities (mostly for use by apps, as Android doesn't provide a command line interface by default), replaced similar "Toolbox" collection.[147]

Open-source community

Android has an active community of developers and enthusiasts who use the Android Open Source Project (AOSP) source code to develop and distribute their own modified versions of the operating system.[148] These community-developed releases often bring new features and updates to devices faster than through the official manufacturer/carrier channels, with a comparable level of quality;[23] provide continued support for older devices that no longer receive official updates; or bring Android to devices that were officially released running other operating systems, such as the HP TouchPad. Community releases often come pre-rooted and contain modifications not provided by the original vendor, such as the ability to overclock or over/undervolt the device's processor.[149] CyanogenMod is the most widely used community firmware,[150] and acts as a foundation for numerous others. There have also been attempts with varying degrees of success to port Android to iPhones, notably the iDroid Project.[151]
Historically, device manufacturers and mobile carriers have typically been unsupportive of third-party firmware development. Manufacturers express concern about improper functioning of devices running unofficial software and the support costs resulting from this.[152] Moreover, modified firmwares such as CyanogenMod sometimes offer features, such as tethering, for which carriers would otherwise charge a premium. As a result, technical obstacles including locked bootloaders and restricted access to root permissions are common in many devices. However, as community-developed software has grown more popular, and following a statement by the Librarian of Congress in the United States that permits the "jailbreaking" of mobile devices,[153] manufacturers and carriers have softened their position regarding third party development, with some, including HTC,[152]Motorola,[154] Samsung[155][156] and Sony,[157] providing support and encouraging development. As a result of this, over time the need to circumvent hardware restrictions to install unofficial firmware has lessened as an increasing number of devices are shipped with unlocked or unlockable bootloaders, similar to Nexus series of phones, although usually requiring that users waive their devices' warranties to do so.[152] However, despite manufacturer acceptance, some carriers in the US still require that phones are locked down, frustrating developers and customers.[158]


Update schedule Linux kernel of android operating system

Update schedule

See also: Android version history
Google provides major incremental upgrades to Android every six to nine months, with confectionery-themed names, which most devices are capable of receiving over the air.[104]The latest major release is Android 6.0 "Marshmallow".
Compared to its primary rival mobile operating system, iOS, Android updates typically reach various devices with significant delays. Except for devices with the Google Nexusbrand, updates often arrive months after the release of the new version, or not at all.[105] This is partly due to the extensive variation in hardware of Android devices, to which each upgrade must be specifically tailored, as the official Google source code only runs on their own Nexus devices. Porting Android to specific hardware is a time- and resource-consuming process for device manufacturers, who prioritize their newest devices and often leave older ones behind.[105] Hence, older smartphones are frequently not updated if the manufacturer decides it is not worth the investment of resources, although the device may be compatible. This problem is compounded when manufacturers customize Android with their own interface and apps, which must be reapplied to each new release. Additional delays can be introduced by wireless carriers who, 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.[105]
The lack of after-sale support from manufacturers and carriers has been widely criticized by consumer groups and the technology media.[106][107] 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,[108] an attitude described as "insulting".[107] The Guardian complained that the method of distribution for updates is complicated only because manufacturers and carriers have designed it that way.[107] 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;[109] however, there has not been another official word about that alliance since its announcement.[105][110]
In 2012 Google began decoupling certain aspects of the operating system (particularly core applications) so they could be updated through Google Play Store independently of the operating system. One of these components, Google Play Services, is a closed-source system-level process providing APIs for Google services, installed automatically on nearly all devices running Android version 2.2 and higher. With these changes, Google can add new operating system functionality through Play Services and application updates without having to distribute an upgrade to the operating system itself. As a result, Android 4.2 and 4.3 contained relatively fewer user-facing changes, focusing more on minor changes and platform improvements.[3][111]

Linux kernel

Android's kernel is based on one of the Linux kernel's long-term support (LTS) branches. Since April 2014, Android devices mainly use versions 3.4 or 3.10 of the Linux kernel.[112][113] The specific kernel version depends on the actual Android device and its hardware platform;[114][115][116] Android has used various kernel versions since the version 2.6.25 that was used in Android 1.0.[41]
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 Binder, ashmem, pmem, logger, wakelocks, and different out-of-memory (OOM) handling.[117][118][119] Certain features that Google contributed back to the Linux kernel, notably a power management feature called "wakelocks", were rejected by mainline kernel developers partly because they felt that Google did not show any intent to maintain its own code.[120][121][122] Google announced in April 2010 that they would hire two employees to work with the Linux kernel community,[123] 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.[121] Some Google Android developers hinted that "the Android team was getting fed up with the process," because they were a small team and had more urgent work to do on Android.[124]
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".[125] 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.[126] 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).[127]Google maintains a public code repository that contains their experimental work to re-base Android off the latest stable Linux versions.[128][129]
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.[130]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,[131] but also by malicious parties to install viruses and malware.[132]
Android is a Linux distribution according to the Linux Foundation,[133] Google's open-source chief Chris DiBona,[134] and several journalists.[135][136] 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.[137]