Android is an operating system for mobile devices such as cellular phones, tablet computers and netbooks. Android was developed by Google and based upon the Linux kernel and GNU software. It was initially developed by Android Inc. (a firm later purchased by Google) and lately by the Open Handset Alliance. According to NPD Group, unit sales for Android OS smartphones ranked second among all smartphone OS handsets sold in the U.S. in the first quarter of 2010. BlackBerry OS holds 36% and iOS holds 21% ranked first and third respectively with Android at second with 28%. A Nielsen report for the same quarter placed Android in fourth place with 9% of the market.
Android has a large community of developers writing apps that extend the functionality of the devices. There are currently over 70,000 apps available for Android, which makes it the second most popular mobile development target. Developers write managed code in the Java language, controlling the device via Google-developed Java libraries.
The unveiling of the Android distribution on 5 November 2007 was announced with the founding of the Open Handset Alliance, a consortium of 71 hardware, software, and telecom companies devoted to advancing open standards for mobile devices. Google released most of the Android code under the Apache License, a free software and open source license.
The Android operating system software stack consists of Java applications running on a Java based object oriented application framework on top of Java core libraries running on a Dalvik virtual machine featuring JIT compilation. Libraries written in C include the surface manager, OpenCore media framework, SQLite relational database management system, OpenGL ES 2.0 3D graphics API, WebKit layout engine, SGL graphics engine, SSL, and Bionic libc. The Android operating system consists of 12 million lines of code including 3 million lines of XML, 2.8 million lines of C, 2.1 million lines of Java, and 1.75 million lines of C++.
- 1 History
- 2 Features
- 3 Hardware running Android
- 4 Software development
- 5 Marketing
- 6 Restrictions and issues
- 7 See also
- 8 References
- 9 Bibliography
- 10 External links
Early acquisition by Google
In July 2005, Google acquired Android, Inc., a small startup company based in Palo Alto, California, USA. Android's co-founders who went to work at Google included Andy Rubin (co-founder of Danger), Rich Miner (co-founder of Wildfire Communications, Inc.), Nick Sears (once VP at T-Mobile), and Chris White (headed design and interface development at WebTV). At the time, little was known about the functions of Android, Inc. other than that they made software for mobile phones. This began rumors that Google was planning to enter the mobile phone market.
At Google, the team led by Rubin developed a mobile device platform powered by the Linux kernel which they marketed to handset makers and carriers on the premise of providing a flexible, upgradeable system. It was reported that Google had already 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. More speculation that Google would be entering the mobile-phone market came in December 2006. 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. More speculation followed reporting that as Google was defining technical specifications, it was showing prototypes to cell phone manufacturers and network operators.
Open Handset Alliance
On 5 November 2007, the Open Handset Alliance, a consortium of several companies which include Texas Instruments, Broadcom Corporation, Google, HTC, Intel, LG, Marvell Technology Group, Motorola, Nvidia, Qualcomm, Samsung Electronics, Sprint Nextel and T-Mobile was unveiled with the goal to develop open standards for mobile devices. Along with the formation of the Open Handset Alliance, the OHA also unveiled their first product, Android, a mobile device platform built on the Linux kernel version 2.6.
On 9 December 2008, it was announced that 14 new members would be joining the Android project, including PacketVideo, ARM Holdings, Atheros Communications, Asustek Computer Inc, Garmin Ltd, Softbank, Sony Ericsson, Toshiba Corp, and Vodafone Group Plc.
With the exception of brief update periods, Android has been available as open source since 21 October 2008. Google opened the entire source code (including network and telephony stacks) under an Apache License.
With the Apache License, vendors can add proprietary extensions without submitting those back to the open source community.
Android has seen a number of updates since its original release. These updates to the base operating system typically fix bugs and add new features.
||Released 9 February 2009|
| 1.5 (Cupcake)
Based on Linux Kernel 2.6.27
| On 30 April 2009, the official 1.5 (Cupcake) update for Android was released. There were several new features and UI updates included in the 1.5 update:
| 1.6 (Donut)
Based on Linux Kernel 2.6.29
| On 15 September 2009, the 1.6 (Donut) SDK was released. Included in the update were:
| 2.0/2.1 (Eclair)
Based on Linux Kernel 2.6.29
| On 26 October 2009 the 2.0 (Eclair) SDK was released. Among the changes were:
The 2.0.1 SDK was released on 3 December 2009.
The 2.1 SDK was released on 12 January 2010.
| 2.2 (Froyo)
Based on Linux Kernel 2.6.32
| On 20 May 2010 the 2.2 (Froyo) SDK was released. Changes included:
| 2.3 (Gingerbread)
Based on Linux Kernel 2.6.33 or 34
| Tentatively scheduled for Q4 2010 launch. Confirmed new features:
Unconfirmed new features:
|Handset layouts||The platform is adaptable to larger, VGA, 2D 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/EDGE, IDEN, CDMA, EV-DO, UMTS, Bluetooth, Wi-Fi, and WiMAX.|
|Messaging||SMS and MMS are available forms of messaging, including threaded text messaging and now Android Cloud to Device Messaging Framework(C2DM) is also a part of Android Push Messaging service.|
|Java support||While Android applications are written in Java, there's no Java Virtual Machine in the platform and Java byte code is not executed. Java classes get recompiled into Dalvik executable and run on Dalvik virtual machine. Dalvik is a specialized virtual machine designed specifically for Android and optimized for battery-powered mobile devices with limited memory and CPU. Android does not support J2ME, like some other mobile operating systems.|
|Media support||Android supports the following audio/video/still media formats: H.263, H.264 (in 3GP or MP4 container), MPEG-4 SP, AMR, AMR-WB (in 3GP container), AAC, HE-AAC (in MP4 or 3GP container), MP3, MIDI, Ogg Vorbis, WAV, JPEG, PNG, GIF, BMP.|
|Additional hardware support||Android can use video/still cameras, touchscreens, GPS, accelerometers, magnetometers, accelerated 2D bit blits (with hardware orientation, scaling, pixel format conversion) and accelerated 3D graphics.|
|Development environment||Includes a device emulator, tools for debugging, memory and performance profiling, and a plugin for the Eclipse IDE.|
|Market||Like many phone-based application stores, the Android Market is a catalog of applications that can be downloaded and installed to target hardware over-the-air, without the use of a PC. Originally only free applications were supported. Paid-for applications have been available on the Android Market in the United States since 19 February 2009. The Android Market has been expanding rapidly. As of April 30, 2010, it had over 50,000 Android applications for download.|
|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). Google has since released an update for the Nexus One and the Motorola Droid which enables multi-touch natively.|
|Bluetooth||Support for A2DP and AVRCP were added in version 1.5; sending files (OPP) and accessing the phone book (PBAP) were added in version 2.0; and voice dialing and sending contacts between phones were added in version 2.2.|
|Videocalling||Not supported by default but as seen with the HTC Evo 4G, handset manufacturers can build front-facing cameras into their phones, so Qik, a software from the Android Market can use it for video-calling. 模板:Citation needed|
|Multitasking||Multitasking of applications is available.|
Hardware running Android
The early feedback on developing applications for the Android platform was mixed. Issues cited include bugs, lack of documentation, inadequate QA infrastructure, and no public issue-tracking system. (Google announced an issue tracker on 18 January 2008.) In December 2007, MergeLab mobile startup founder Adam MacBeth stated, "Functionality is not there, is poorly documented or just doesn't work... It's clearly not ready for prime time." Despite this, Android-targeted applications began to appear the week after the platform was announced. The first publicly available application was the Snake game. The Android Dev Phone is a SIM-unlocked and hardware-unlocked device that is designed for advanced developers. While developers can use regular consumer devices purchased at retail to test and use their applications, some developers may choose not to use a retail device, preferring an unlocked or no-contract device.
Software development kit
The Android SDK includes a comprehensive set of development tools. These include a debugger, libraries, a handset emulator (based on QEMU), documentation, sample code, and tutorials. Currently supported development platforms include x86-architecture computers running Linux (any modern desktop Linux distribution), Mac OS X 10.4.8 or later, Windows XP or Vista. Requirements also include Java Development Kit, Apache Ant, and Python 2.2 or later. The officially supported integrated development environment (IDE) is Eclipse (3.2 or later) using the Android Development Tools (ADT) Plugin, though developers may use any text editor to edit Java and XML files then use command line tools to create, build and debug Android applications as well as control attached Android devices (e.g., triggering a reboot, installing software package(s) remotely).
A preview release of the Android software development kit (SDK) was released on 12 November 2007. On 15 July 2008, the Android Developer Challenge Team accidentally sent an email to all entrants in the Android Developer Challenge announcing that a new release of the SDK was available in a "private" download area. The email was intended for winners of the first round of the Android Developer Challenge. The revelation that Google was supplying new SDK releases to some developers and not others (and keeping this arrangement private) has led to widely reported frustration within the Android developer community.
On 18 August 2008 the Android 0.9 SDK beta was released. This release provided an updated and extended API, improved development tools and an updated design for the home screen. Detailed instructions for upgrading are available to those already working with an earlier release. On 23 September 2008 the Android 1.0 SDK (Release 1) was released. According to the release notes, it included "mainly bug fixes, although some smaller features were added". It also included several API changes from the 0.9 version.
On 9 March 2009, Google released version 1.1 for the Android dev phone. While there are a few aesthetic updates, a few crucial updates include support for "search by voice, priced applications, alarm clock fixes, sending gmail freeze fix, fixes mail notifications and refreshing intervals, and now the maps show business reviews". Another important update is that Dev phones can now access paid applications and developers can now see them on the Android Market.
In the middle of May 2009, Google released version 1.5 (Cupcake) of the Android OS and SDK. This update included many new features including video recording, support for the stereo bluetooth profile, a customizable onscreen keyboard system and voice recognition. This release also opened up the AppWidget framework to third party developers allowing anyone to create their own home screen widgets.
In September 2009 the "Donut" version (1.6) was released which featured better search, battery usage indicator and VPN control applet. New platform technologies included Text to Speech engine (not available on all phones), Gestures & Accessibility framework.
Android Applications are packaged in .apk format and stored under
/data/app folder on the Android OS. The user can run the command
adb root to access this folder as only the root has permissions to access this folder.
App Inventor for Android
On July 12, 2010 Google announced the availability of App Inventor for Android, a Web-based visual development environment for novice programmers, based on MIT's Open Blocks Java library and providing access to Android devices' GPS, accelerometer and orientation data, phone functions, text messaging, speech-to-text conversion, contact data, persistent storage, and Web services, initially including Amazon and Twitter.  "We could only have done this because Android’s architecture is so open," said the project director, MIT's Hal Abelson. Under development for over a year, the block-editing tool has been taught to non-majors in computer science at Harvard, MIT, Wellsley, and the University of San Francisco, where professor David Wolber developed an introductory computer science course and tutorial book for non-computer science students based on App Inventor for Android.
Android Developer Challenge
The Android Developer Challenge was a competition for the most innovative application for Android. Google offered prizes totaling 10 million US dollars, distributed between ADC I and ADC II. ADC I accepted submissions from 2 January to 14 April 2008. The 50 most promising entries, announced on 12 May 2008, each received a $25,000 award to fund further development. It ended in early September with the announcement of ten teams that received $275,000 each, and ten teams that received $100,000 each. ADC II was announced on 27 May 2009. The first round of the ADC II closed on 6 October 2009. The first-round winners of ADC II comprising the top 200 applications were announced on 5 November 2009. Voting for the second round also opened on the same day and ended on November 25. Google announced the top winners of ADC II on November 30, with SweetDreams, What the Doodle!? and WaveSecure being nominated the overall winners of the challenge.
Google has also participated in the Android Market by offering several applications for its services. These applications include Google Voice for the Google Voice service, Sky Map for watching stars, Finance for their finance service, Maps Editor for their MyMaps service, Places Directory for their Local Search, Google Goggles that searches by image, Google Translate, Google Shopper, Listen for podcasts and My Tracks, a jogging application.
Third party applications
With the growing number of Android handsets, there has also been an increased interest by third party developers to port their applications to the Android operating system. Famous applications that have been converted to the Android operating system include Shazam, Backgrounds, and WeatherBug.
The Android operating system has also been considered important enough模板:Weasel-inline by a lot of the most popular internet sites and services to create native applications. These include MySpace, Facebook, and Twitter.
Libraries written in C and other languages can be compiled to ARM native code and installed using the Android Native Development Kit. Native classes can be called from Java code running under the Dalvik VM using the
System.loadLibrary call, which is part of the standard Android Java classes.
Complete applications can be compiled and installed using traditional development tools. The ADB debugger gives a root shell under the Android Emulator which allows native ARM code to be uploaded and executed. ARM code can be compiled using GCC on a standard PC. Running native code is complicated by the fact that Android uses a non-standard C library (known as Bionic). The underlying graphics device is available as a framebuffer at /dev/graphics/fb0. The graphics library that Android uses to arbitrate and control access to this device is called the Skia Graphics Library (SGL), and it has been released under an open source license. Skia has backends for both win32 and Unix, allowing the development of cross-platform applications, and it is the graphics engine underlying the Google Chrome web browser.
There is a community of open-source enthusiasts that build and share Android-based firmware with a number of customizations and additional features, such as FLAC lossless audio support and the ability to store downloaded applications on the microSD card. This usually involves rooting the device. Rooting lets users load modified firmwares allowing users of older phones to use applications available only on newer releases.
Those firmware packages are updated frequently, incorporate elements of Android functionality that haven't yet been officially released within a carrier-sanctioned firmware, and tend to have fewer limitations. CyanogenMod is one such firmware.
On 24 September 2009, Google issued a cease and desist letter to the modder Cyanogen, citing issues with the re-distribution of Google's closed-source applications within the custom firmware. Even though Android OS is open source, phones come packaged with closed-source Google applications for functionality such as the application store and GPS navigation. Google has asserted that these applications can only be provided through approved distribution channels by licensed distributors. Cyanogen has complied with Google's wishes and is continuing to distribute this mod without the proprietary software. He has provided a method to back up licensed Google applications during the mod's install process and restore them when it is complete.
Android Green is the color of the Android Robot that represents the Android operating system. The print color is PMS 376C and the online hex color is #A4C639, as specified by the Android Brand Guidelines.
The custom typeface of Android is called Norad, only used in the text logo.
In February 2010 ComScore ranked the Android platform as obtaining a 9.0% of the smartphone platform marketshare. This figure was up from an earlier estimate of 5.2% stated in November 2009. In July 2010 ComScore revised Android's share for 3 months March/April/May 2010 to 13.0%, an increase of 4 percentage points, 0.2 percentage points behind Microsoft whose share had dropped 1.9%.
In October 2009, Gartner Inc. predicted that by 2012, Android would become the world's second most popular smartphone platform, behind Nokia's Symbian OS, which is very popular outside the US. Meanwhile, BlackBerry would fall from 2nd to 5th place, iPhone would remain in 3rd place, and Microsoft's Windows Mobile would remain in 4th place.
In May 2010, Android's first quarter US sales surpassed that of the rival iPhone platform. According to a report by the NPD group, Android achieved 28% smartphone sales in the US market, up 8% from the December quarter. The iPhone's sales were flat at 21% over the same reporting period.
According to an interview with Eric Schmidt in The Guardian, Android is getting 160,000 new users per day (end June 2010) up from 100,000 per day in May 2010.
Restrictions and issues
- Android's kernel was derived from Linux but has been tweaked by Google outside the main Linux kernel tree. Android does not have a native X Window System nor does it support the full set of standard GNU libraries and this makes it difficult to port existing GNU/Linux applications or libraries to Android.
- Google no longer maintains the code they previously contributed to the Linux kernel as part of their Android effort, effectively branching kernel code in their own tree, separating their code from Linux. The code which is no longer maintained was deleted in January 2010 from the Linux codebase. However, Google announced in April 2010 that they will employ staff to work with the Linux kernel community.
- Android did not support setting up a network proxy configuration for WiFi connections until Android 2.1 (Eclair).
- Android does not support EAP extensions under WPA- and WPA2- Enterprise.
- Android does not support Cisco-compatible IPsec virtual private networks (Layer 2 Tunneling Protocol is supported).
- Android did not support wireless ad hoc networking until Android 2.2 (Froyo).
Issues concerning application development
- Android does not use established Java standards, i.e. Java SE and ME. This prevents compatibility among Java applications written for those platforms and those for the Android platform. Android only reuses the Java language syntax, but does not provide the full-class libraries and APIs bundled with Java SE or ME. However, the Myriad Group claim that their new J2Android tool can convert Java MIDlets into Android applications.
- Developers have reported that it is difficult to maintain applications on multiple versions of Android, owing to compatibility issues between versions 1.5 and 1.6, especially the different resolution ratios in use among various Android phones. Such problems were poignantly brought into focus as they were encountered during the ADC2 contest.
- The rapid growth in the number of Android-based phone models with differing hardware capabilities also makes it difficult to develop applications that work on all Android-based phones. As of June 2010, 50% of Android phones run the 2.1 version, and 24.6% still run the 1.5 version
- Older versions of Android do not readily support Bluetooth file exchange, although it may still be achieved with some hacking. Bluetooth is supported by more recent phones.
- Android does not support video calls as do other mobile operating systems, such as Symbian OS and Windows Mobile, although third-party, applications like Qik allow video calling on some models, and video broadcasting on others.
Using the native Google Calendar functionality for Android phones, an Android device user runs into the same limitations that exist in the Calendar application. The most noticeable defect is the lack of proper time zone support: it is not possible to set the time zone for start/end times of events. Because of this issue, users experience difficulty while traveling with Android devices.
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- Official Android page
- Google Projects for Android from Google Code
- Android Wiki