Dalvik virtual machine and apk Extention

Dalvik virtual machine

Android program is mainly run on the Dalvik environment that is DALVIK VIRTUAL MACHINE. Dalvik Virtual Machine is  register based virtual machine,designed and written by Dan Borstin with the contribution of Google engineers.
Features

• It is optimized for low memory requirements.
• It designed to multiple VM instance to run at once
• It also support for process isolation
• Memmory management and Threading support

A tool named dx, included in the Android SDK, transforms the Java Class files of Java classes compiled by a regular Java compiler into another class file format (the .dex format).

APK (Android application package)

APK is the file format used to distribute and install application software and middleware onto Google's Android operating system that is android devices like phone and tabs. To build an APK file, a program for Android is first compiled, and then all of its parts are packaged into one file that file which hold the apk extension. and also holds all of that program's code such as (.dex files), resources, assets, certificates, and manifest file. As is the case with many file formats, APK files can have any name needed, but must end with the four character, three letter extension, .apk.