Dalvik virtual machine. It is a type of JVM used in Android devices to run apps, and is optimised for low processing power and low memory environments. Unlike JVM, Dalvik virtual machine (VM) does not run .class files, instead it runs .dex files. Dex files are built from .class file at the time of compilation and provide higher efficiency in low-resource environments. Dalvik VM (DVM) allows multiple instances of virtual machines to be created simultaneously, providing security, isolation, memory management and threading support.

ART. Google has introduced a new virtual machine known as ART, which is short for Android Runtime, in their newer releases of Android. In 5.0, DVM is completely replaced by ART.

ART has many advantages over DVM such as Ahead of Time (AOT) compilation and improved garbage collection, which boost the performance of apps significantly.

Core Java libraries. These are different from Java SE and Java ME libraries. However, these libraries provide most functionalities defined in Java SE libraries.

Application framework. These are the blocks that our applications directly interact with. These programs manage the basic functions of phone like resource management and voice-call management.

Important blocks of Application framework are:
Activity manager. Manages the activity life cycle of applications
Content providers. Manages data sharing between applications
Telephony manager. Manages all voice calls. We use telephony manager if we want to access voice calls in our application
Location manager. Manages location using GPS or a mobile tower
Resource manager. Manages various types of resources we use in our application

Applications. Applications form the top layer in Android architecture. Several standard applications come pre-installed with every device such as SMS client app, Dialer, Web browser and Contacts Manager.

Firefox OS
Firefox OS is a Linux kernel based open source OS for smartphones and tablet computers; it is set to be used on smart TVs. It is being developed by Mozilla, the non-profit organisation best known for Firefox Web browser.

Firefox OS is designed to provide a complete, community based alternative system for mobile devices, using open standards and approaches such as HTML5 applications, JavaScript—a robust privilege model, open Web APIs to communicate directly with mobile phone hardware and application marketplace.

Windows Phone

Fig. 13: Ubuntu Touch Home screen

Windows is a family of mobile OSes developed by Microsoft for smartphones as the replacement successor to Windows Mobile.

Windows Phone features a new UI derived from Metro design language. Unlike Windows Mobile, it is primarily aimed at the consumer market rather than the enterprise market.

Blackberry OS
BlackBerry OS is a proprietary mobile OS developed by BlackBerry Ltd for its BlackBerry line of smartphones. The OS provides multitasking and supports specialised input devices that have been adopted by BlackBerry Ltd for use in its handhelds, particularly the trackwheel, trackball and, most recently, trackpad and touchscreen.

Ubuntu Touch
Ubuntu Touch, also known as Ubuntu Phone, is a mobile version of Ubuntu OS developed by Canonical UK Ltd and Ubuntu Community. It is designed primarily for touchscreen mobile devices such as smartphones and tablet computers.

Ubuntu Touch was released to manufacturers on September 16, 2014. Aquaris E4.5, the world’s first Ubuntu based smartphone, went on sale in Europe on February 9, 2015.

Future prospects
With changing trends in the chipset industry, OS developers are not far behind. Software packages and applications are being developed to meet the demands of users and also to incorporate hardware additions like touch sensor, look-away to pause, etc. We might be seeing facial-recognition or retina-scanner software packages in the future.



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