Tuesday, May 8, 2012

Android (operating system)


Android
Android robot.svgAndroid logo.png
Android 4.0.png
Home screen displayed by Samsung Galaxy Nexus, running Android 4.0 "Ice Cream Sandwich"
Company /developerGoogle IncOpen Handset Alliance,Android Open Source Project
Programmed inC (core),[1] Java (UI), C++
OS familyLinux
Working stateCurrent
Source modelOpen Source[2]
Initial release20 September 2008
Latest stable release4.0.4 (Ice Cream Sandwich)[3] / 28 March 2012; 41 days ago
Latest unstable release4.0.5
Package managerGoogle Play / APK
Supported platformsARMMIPS,[4] x86[5]
Kernel typeMonolithic (modified Linux kernel)
Default user interfaceGraphical
LicenseApache License 2.0
Linux kernel patches under GNU GPL v2[6]
Official website

Android is a Linux-based operating system for mobile devices such as smartphones and tablet computers. It is developed by the Open Handset Alliance, led by Google, and other companies.[2]
Google purchased the initial developer of the software, Android Inc., in 2005.[7] The unveiling of the Android distribution in 2007 was announced with the founding of the Open Handset Alliance, a consortium of 86 hardware, software, andtelecommunication companies devoted to advancing open standards for mobile devices.[8] Google releases the Android code as open-source, under the Apache License.[9] The Android Open Source Project (AOSP) is tasked with the maintenance and further development of Android.[10]
Android has a large community of developers writing applications ("apps") that extend the functionality of the devices. Developers write primarily in a customized version of Java.[11] Apps can be downloaded from third-party sites or through online stores such as Google Play (formerly Android Market), the app store run by Google. In October 2011, there were more than 500,000 apps available for Android,[12] and the estimated number of applications downloaded from the Android Market as of December 2011 exceeded 10 billion.[13]
Android was listed as the best-selling smartphone platform worldwide in Q4 2010 by Canalys[14][15] with over 300 million Android devices in use by February 2012.[16] According to Google's Andy Rubin, as of December 2011, there were over 700,000 Android devices activated every day.

History

Foundation

Android, Inc. was founded in Palo Alto, California, United States in October, 2003 by Andy Rubin (co-founder of Danger),[18] Rich Miner (co-founder of Wildfire Communications, Inc.),[19] Nick Sears (once VP at T-Mobile),[20] and Chris White (headed design and interface development at WebTV)[7] to develop, in Rubin's words "...smarter mobile devices that are more aware of its owner's location and preferences".[7] Despite the obvious past accomplishments of the founders and early employees, Android Inc. operated secretly, revealing only that it was working on software for mobile phones.[7] 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.[21]

Acquisition by Google

Google acquired Android Inc. on August 17, 2005, making Android Inc. a wholly owned subsidiary of Google Inc. Key employees of Android Inc., including Andy Rubin, Rich Miner and Chris White, stayed at the company after the acquisition.[7]Not much was known about Android Inc. at the time of the acquisition, but many assumed that Google was planning to enter the mobile phone market with this move.[7]

Post-acquisition development

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.[22][23][24]
Speculation about Google's intention to enter the mobile communications market continued to build through December 2006.[25] Reports from the BBC and The Wall Street Journal noted that Google wanted its search and applications on mobile phones and it was working hard to deliver that. Print and online media outlets soon reported rumors that Google was developing a Google-branded handset. Some speculated that as Google was defining technical specifications, it was showing prototypes to cell phone manufacturers and network operators.
In September 2007, InformationWeek covered an Evalueserve study reporting that Google had filed several patent applications in the area of mobile telephony.[26][27]

Open Handset Alliance

On November 5, 2007, the Open Handset Alliance, a consortium of several companies which include Broadcom CorporationGoogleHTCIntelLGMarvell Technology GroupMotorolaNvidiaQualcommSamsung ElectronicsSprint Nextel,T-Mobile and Texas Instruments unveiled itself. The goal of the Open Handset Alliance is to develop open standards for mobile devices.[8] On the same day, the Open Handset Alliance also unveiled their first product, Android, a mobile deviceplatform built on the Linux kernel version 2.6.[8]

Android Open Source Project

The Android Open Source Project (AOSP) is led by Google, and is tasked with the maintenance and development of Android.[30] According to the project "The goal of the Android Open Source Project is to create a successful real-world product that improves the mobile experience for end users."[31] AOSP also maintains the Android Compatibility Program, defining an "Android compatible" device "as one that can run any application written by third-party developers using the Android SDK and NDK", to prevent incompatible Android implementations.[31] The compatibility program is also optional and free of charge, with the Compatibility Test Suite also free and open-source.[32]

Version history

Android has seen a number of updates since its original release, each fixing bugs and adding new features. Each version is named, in alphabetical order, after a dessert.[33]
Recent releases
  • 2.3 Gingerbread refined the user interface, improved the soft keyboard and copy/paste features, better native code support (which improves gaming performance), added SIP support (VoIP calls), and added support for Near Field Communication.[34]
  • 3.0 Honeycomb was a tablet-oriented[35][36][37] release which supports larger screen devices and introduces many new user interface features, support for multi-core processors, hardware acceleration for graphics[37] and full system encryption.[38][39] The first device featuring this version, the Motorola Xoom tablet, went on sale in February 2011.[40][41]
  • 3.1 Honeycomb, released in May 2011, added support for extra input devices, USB host mode for transferring information directly from cameras and other devices, and the Google Movies and Books apps.[42]
  • 3.2 Honeycomb, released in July 2011, added optimization for a broader range of screen sizes, new "zoom-to-fill" screen compatibility mode, loading media files directly from SD card, and an extended screen support API.[43] Huawei MediaPad is the first 7 inch tablet to use this version[44]
  • 4.0 Ice Cream Sandwich, announced on October 19, 2011, brought Honeycomb features to smartphones and added new features including facial recognition unlock, network data usage monitoring and control, unified social networking contacts, photography enhancements, offline email searching, app folders, and information sharing using NFC. Android 4.0.4 is the latest Android version that is available to phones. The source code of Android 4.0.1 was released on November 14, 2011.[45]

Design

Architecture diagram
Android consists of a kernel based on the Linux kernel, with middlewarelibraries and APIs written in C and application software running on an application framework which includes Java-compatible libraries based on Apache Harmony. Android uses the Dalvik virtual machine with just-in-time compilation to run Dalvik dex-code (Dalvik Executable), which is usually translated from Java bytecode.[46]
The main hardware platform for Android is the ARM architecture. There is support for x86 from the Android x86 project,[5] and Google TV uses a special x86 version of Android.

Linux

Android's kernel is based on the Linux kernel and has further architecture changes by Google outside the typical Linux kernel development cycle.[47] Android does not have a native X Window System nor does it support the full set of standard GNUlibraries, and this makes it difficult to port existing Linux applications or libraries to Android.[48]
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 kernel maintainers felt that Google did not show any intent to maintain their own code.[49][50][51] Even though Google announced in April 2010 that they would hire two employees to work with the Linux kernel community,[52] 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.[50] 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.[53]
However, in September 2010, Linux kernel developer Rafael J. Wysocki added a patch that improved the mainline Linux wakeup events framework. He said that Android device drivers that use wakelocks can now be easily merged into mainline Linux, but that Android's opportunistic suspend features should not be included in the mainline kernel.[54][55] 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".[56]
In December 2011, Greg Kroah-Hartman announced the start of the Android Mainlining Project, which aims to put some Android drivers, patches and features back into the Linux kernel, starting in Linux 3.3.[57] further integration being expected for Linux Kernel 3.4.[58]

Features

The Android Emulator default home screen (v1.5)
Current features and specifications:[59][60][61]
Handset layouts
The platform is adaptable to larger, VGA2D graphics library, 3D graphics library based on OpenGL ES 2.0 specifications, and traditional smartphone layouts.
Storage
SQLite, a lightweight relational database, is used for data storage purposes.
Connectivity
Android supports connectivity technologies including GSM/EDGEIDENCDMAEV-DOUMTSBluetoothWi-FiLTENFC and WiMAX.
Messaging
SMS and MMS are available forms of messaging, including threaded text messaging and now Android Cloud To Device Messaging (C2DM) is also a part of Android Push Messaging service.
Multiple language support
Android supports multiple languages.[34]
Web browser
The web browser available in Android is based on the open-source WebKit layout engine, coupled with Chrome's V8 JavaScript engine. The browser scores 100/100 on the Acid3 test on Android 4.0.
Java support
While most Android applications are written in Java, there is no Java Virtual Machine in the platform and Java byte code is not executed. Java classes are compiled into Dalvik executables and run on Dalvik, a specialized virtual machine designed specifically for Android and optimized for battery-powered mobile devices with limited memory and CPU. J2ME support can be provided via third-party applications.
Media support
Android supports the following audio/video/still media formats: WebMH.263H.264 (in 3GP or MP4 container), MPEG-4 SPAMRAMR-WB (in 3GP container), AACHE-AAC (in MP4 or 3GP container), MP3MIDIOgg VorbisFLACWAVJPEG,PNGGIFBMPWebP.[61]
Streaming media support
RTP/RTSP streaming (3GPP PSSISMA), HTML progressive download (HTML5 ). Adobe Flash Streaming (RTMP) and HTTP Dynamic Streaming are supported by the Flash plugin.[62] Apple HTTP Live Streaming is supported by RealPlayer for Android,[63] and by the operating system in Android 3.0 (Honeycomb).[37]
Additional hardware support
Android can use video/still cameras, touchscreensGPSaccelerometersgyroscopesbarometersmagnetometers, dedicated gaming controls, proximity and pressure sensorsthermometers, accelerated 2D bit blits (with hardware orientation, scaling, pixel format conversion) and accelerated 3D graphics.
Multi-touch
Android has native support for multi-touch which was initially made available in handsets such as the HTC Hero. The feature was originally disabled at the kernel level (possibly to avoid infringing Apple's patents on touch-screen technology at the time).[64] Google has since released an update for the Nexus One and the Motorola Droid which enables multi-touch natively.[65]
Bluetooth
Supports A2DPAVRCP, sending files (OPP), accessing the phone book (PBAP), voice dialing and sending contacts between phones. Keyboard, mouse and joystick (HID) support is available in Android 3.1+, and in earlier versions through manufacturer customizations and third-party applications.[66]
Video calling
Android does not support native video calling, but some handsets have a customized version of the operating system that supports it, either via the UMTS network (like the Samsung Galaxy S) or over IP. Video calling through Google Talk is available in Android 2.3.4 and later. Gingerbread allows Nexus S to place Internet calls with a SIP account. This allows for enhanced VoIP dialing to other SIP accounts and even phone numbers. Skype 2.1 offers video calling in Android 2.3, including front camera support.
Multitasking
Multitasking of applications, with unique handling of memory allocation, is available.[67]
Voice based features
Google search through voice has been available since initial release.[68] Voice actions for calling, texting, navigation, etc. are supported on Android 2.2 onwards.[69]
Tethering
Android supports tethering, which allows a phone to be used as a wireless/wired Wi-Fi hotspot. Before Android 2.2 this was supported by third-party applications or manufacturer customizations.[70]
Screen capture
Android supports capturing a screenshot by pressing the power and volume-down buttons at the same time.[71] Prior to Android 4.0, the only methods of capturing a screenshot were through manufacturer and third-party customizations or otherwise by using a PC connection (DDMS developer's tool). These alternative methods are still available with the latest Android.
External storage
Most Android devices include microSD slot and can read microSD cards formatted with FAT32Ext3fs or Ext4fs file system. To allow use of high-capacity storage media such as USB flash drives and USB HDDs, many Android tablets also include USB 'A' receptacle. Storage formatted with FAT32 is handled by Linux Kernel VFAT driver, while 3rd party solutions are required to handle other popular file systems such as NTFSHFS Plus and exFAT.

Uses

The Galaxy Nexus, the latest "Google phone"
Google TV Home Screen
While Android is designed primarily for smartphones and tablets, the open and customizable nature of the operating system allows it to be used on other electronics, including laptops and netbooks,smartbooks,[72] ebook readers,[73] and smart TVs (Google TV). Further, the OS has seen niche applications on wristwatches,[74] headphones,[75] car CD and DVD players,[76] smart glasses (Project Glass), refrigerators, vehicle satnav systems, home automation systems, games consoles, mirrors,[77] cameras,[78] portable media players[79] landlines,[80] and treadmills.[81]
The first commercially available phone to run Android was the HTC Dream, released on 22 October 2008.[82] In early 2010 Google collaborated with HTC to launch its flagship[83] Android device, the Nexus One. This was followed later in 2010 with the Samsung-made Nexus S and in 2011 with the Galaxy Nexus.
iOS and Android 2.3.3 'Gingerbread' may be set up to dual boot on a jailbroken iPhone or iPod Touch with the help of OpeniBoot and iDroid.[84][85]
In December 2011 it was announced the Pentagon has officially approved Android for use by its personnel.[86][87][88]

Applications

Applications are usually developed in the Java language using the Android Software Development Kit, but other development tools are available, including a Native Development Kit 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.
Applications can be acquired by end-users either through a store such as Google Play or the Amazon Appstore, or by downloading and installing the application's APK file from a third-party site.[89]

Google Play

The Play Store on a Galaxy Nexus.
Google Play is an online software store developed by Google for Android devices. An application program ("app") called "Play Store" is preinstalled on most Android devices and allows users to browse and download apps published by third-party developers, hosted on Google Play. As of October 2011, there were more than 500,000 apps available for Android,[12] and the estimated number of applications downloaded from the Play Store as of December 2011 exceeded 10 billion.[13] The operating system itself is installed on 130 million total devices.[90]
Only devices that comply with Google's compatibility requirements are allowed to preinstall and access the Play Store.[91] The app filters the list of available applications to those that are compatible with the user's device, and developers may restrict their applications to particular carriers or countries for business reasons.[92]
Google has participated in the Play Store by offering many free applications themselves, including Google VoiceGoogle Goggles, Gesture Search, Google Translate, Google Shopper, Listen and My Tracks. In August 2010, Google launched "Voice Actions for Android",[93] which allows users to search, write messages, and initiate calls by voice.

Security

An example of app permissions in the Play Store.
Android applications run in a sandbox, an isolated area of the operating system that does not have access to the rest of the system's resources, unless access permissions are granted by the user when the application is installed. Before installing an application, the Play Store displays all required permissions. A game may need to enable vibration, for example, but should not need to read messages or access the phonebook. After reviewing these permissions, the user can decide whether to install the application.[94] The sandboxing and permissions system weakens the impact of vulnerabilities and bugs in applications, but developer confusion and limited documentation has resulted in applications routinely requesting unnecessary permissions, reducing its effectiveness.[95] The complexity of inter-application communication implies Android has a large attack surface.[96]
Several security firms have released antivirus software for Android devices, in particular, AVG Technologies,[97] Avast!,[98] F-Secure,[99] Kaspersky,[100] McAfee[101] and Symantec.[102] This software is ineffective as sandboxing also applies to such applications, limiting their ability to scan the deeper system for threats.[103]

Privacy

Android smartphones have the ability to report the location of Wi-Fi access points, encountered as phone users move around, to build databases containing the physical locations of hundreds of millions of such access points. These databases form electronic maps to locate smartphones, allowing them to run apps like FoursquareLatitudePlaces, and to deliver location-based ads.[104]
Third party monitoring software such as TaintDroid,[105] an academic research-funded project, can, in some cases, detect when personal information is being sent from applications to remote servers.[106]
In March 2012 it was revealed that Android Apps can copy photos without explicit user permission,[107] Google responded they "originally designed the Android photos file system similar to those of other computing platforms like Windows and Mac OS. [...]we're taking another look at this and considering adding a permission for apps to access images. We've always had policies in place to remove any apps [on Google Play] that improperly access your data."[108]

Marketing

The Android logotype was designed along with the Droid font family by Ascender Corporation,[109] the robot icon was designed by Irina Blok.[110]
Android Green is the color of the Android Robot that represents the Android operating system. The print color is PMS 376C and the RGB color value in hexadecimal is #A4C639, as specified by the Android Brand Guidelines.[111] The custom typeface of Android is called Norad (cf. NORAD). It is only used in the text logo.[111]

Market share

Research company Canalys estimated in Q2 2009 that Android had a 2.8% share of worldwide smartphone shipments.[112] By Q4 2010 this had grown to 33% of the market, becoming the top-selling smartphone platform. This estimate includes the Tapas and OMS variants of Android.[15] By Q3 2011 Gartner estimates more than half (52.5%) of the smartphone market belongs to Android.[113]
In February 2010 ComScore said the Android platform had 9.0% of the U.S. smartphone market, as measured by current mobile subscribers. This figure was up from an earlier estimate of 5.2% in November 2009.[114] By the end of Q3 2010 Android's U.S. market share had grown to 21.4%.[115]
In May 2010, Android's first quarter U.S. sales surpassed that of the rival iPhone platform. According to a report by the NPD group, Android achieved 25% smartphone sales in the US market, up 8% from the December quarter. In the second quarter, Apple's iOS was up by 11%, indicating that Android is taking market share mainly from RIM, and still has to compete with heavy consumer demand for new competitor offerings.[116] Furthermore, analysts pointed to advantages that Android has as a multi-channel, multi-carrier OS.[117] In Q4 2010 Android had 59% of the total installed user base of Apple's iOS in the U.S. and 46% of the total installed user base of iOS in Europe.[118][119]
As of June 2011, Google said that 550,000 new Android devices were being activated every day[120] — up from 400,000 per day a month earlier — and more than 100 million devices had been activated.[121] Android hit 300,000 activations per day back in December 2010. By July 14, 2011, 550,000 Android devices were being activated by Google each day, with 4.4% growth per week.[122] On 1 August 2011, Canalys estimated that Android had about 48% of the smartphone market share.[123] On October 13, 2011, Google announced that there were 190 million Android devices in the market.[124] As of November 16, 2011, during the Google Music announcement "These Go to Eleven", 200 million Android devices had been activated.[125] Based on this number, with 1.9% of Android devices being tablets, approximately 3.8 million Android Honeycomb Tablets have been sold.[126] On December 20, 2011, Andy Rubin announced that Google was activating 700,000 new Android devices daily.[17] Two months later, on February 27, 2012, Andy Rubin announced that Google was activating over 850,000 Android smartphones and tablets daily.

Usage share

Usage share of the different versions as of 2 April 2012
Usage share of the different versions as of 1 May 2012.[127]
Version
DistributionAPI level
4.0.x Ice Cream Sandwich14-154.9%
3.x.x Honeycomb11-133.3%
2.3.x Gingerbread9-1064.4%
2.2 Froyo820.9%
2.0, 2.1 Eclair75.5%
1.6 Donut40.7%
1.5 Cupcake30.3%
There were two more internal releases, called "Astro" and "Bender". The code names are in alphabetical order, and were allegedly changed from robots to desserts to avoid trademark issues.[128]

Intellectual property

Licensing

The source code for Android is available under free and open source software licenses. Google publishes most of the code (including network and telephony stacks)[129] under the Apache License version 2.0,[130][131][132] and the rest, Linux kernel changes, under the GNU General Public License version 2.
The Open Handset Alliance develops the changes to the Linux kernel, in public, with source code publicly available at all times. The rest of Android is developed in private, with source code released publicly when a new version is released. Typically Google collaborates with a hardware manufacturer to produce a flagship device (part of the Google Nexus series) featuring the new version of Android, then makes the source code available after that device has been released.[133]
In early 2011, Google chose to temporarily withhold the Android source code to the tablet-only Honeycomb release, the reason, according to Andy Rubin in an official Android blog post, was because Honeycomb was rushed for production of the Motorola Xoom,[134] and they did not want third parties creating a "really bad user experience" by attempting to put onto smartphones a version of Android intended for tablets.[135] The source code was once again made available in November 2011 with the release of Android 4.0.[136]

Patents

Both Android and Android phone manufacturers have been the target of numerous patent lawsuits. On 12 August 2010, Oracle sued Google over claimed infringement of copyrights and patents related to the Java programming language.[137] Specifically, the patent infringement claim references seven United States patents including US 5966702 "Method and apparatus for pre-processing and packaging class files", and US 6910205 "Interpreting functions utilizing a hybrid of virtual and native machine instructions".[138]
In response, Google submitted multiple lines of defense, counterclaiming that Android did not infringe on Oracle's patents or copyright, that Oracle's patents were invalid, and several other defenses. They said that Android is based on Apache Harmony, a clean room implementation of the Java class libraries, and an independently developed virtual machine called Dalvik.[139][140][141]
Microsoft has also sued several manufacturers of Android devices for patent infringement, and collects patent licensing fees from others. In October 2011 Microsoft said they had signed license agreements with ten Android device manufacturers, accounting for 55% of worldwide revenue for Android devices.[142] These include Samsung and HTC.[143]
Google has publicly expressed its dislike for the current patent landscape in the United States, accusing Apple, Oracle and Microsoft of trying to take down Android through patent litigation, rather than innovating and competing with better products and services.[144] In August 2011, Google started the process of purchasing Motorola Mobility for US$12.5 billion, which was viewed in part as a defensive measure to protect Android, since Motorola Mobility holds more than 17,000 patents.[145] In December 2011 Google acquired in the region of a thousand patents from IBM,[146]which may aid in defense against Oracle.