apk (file format)
|Internet media type|
|Type of format||Package format|
|Container for||Android, Blackberry 10 and HarmonyOS under Ark Compiler: Mobile apps|
Windows 11: Desktop apps for WSA
The Android Package with the file extension apk is the file format used by the Android operating system, and a number of other Android-based operating systems for distribution and installation of mobile apps, mobile games and middleware. It can be written in either Java or Kotlin.
APK is analogous to other software packages such as APPX in Microsoft Windows, .app on HAP for HarmonyOS or a Debian package in Debian-based operating systems. To make an APK file, a program for Android is first compiled using a tool such as Android Studio or Visual Studio and then all of its parts are packaged into one container file. An APK file contains all of a 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 it may be required that the file name ends in the file extension for being recognized as such.
Most Android implementations allow users to manually install APK files only after they turn on an "Unknown Sources" setting that allows installation from sources other than trusted ones like Google Play. One may do so for many reasons, such as during the development of apps, to install apps not found on the store, or to install an older version of an existing app.
Use on other operating systems
Blackberry Limited supported Android 4.1 Jelly Bean apps and up through Android Runtime to now discontinued Blackberry 10 through the January 2014 10.2.1 firmware update. On June 18, 2014, BlackBerry announced an official relationship with Amazon.com, which resulted in the 10.3 update bundling the Amazon Appstore.
At the Windows 11 announcement event in June 2021, Microsoft showcased the new Windows Subsystem for Android (WSA) that will enable support for the Android Open Source Project (AOSP) and will allow users to run Android apps on their Windows desktop. Microsoft confirmed users will be able to sideload Android apps onto Windows and that it would be possible to install APK files downloaded from third-party sources.
Google plans to introduce its own way to run Android apps on Windows some time in 2022.
Huawei released it's proprietary operating system HarmonyOS in August 9, 2019 for smart TVs first and later launched for phones and tablets on June 2, 2021 with HarmonyOS 2.0. HarmonyOS under the Linux module of the multi-kernel designed system is compatible with legacy Android apps under the Ark Compiler under the new IoT smart oriented operating system for phones and tablets. It is claimed by the company to improve Android system operation fluency by 24%, response speed by 44%, and the smoothness of the third-party application up to 60%. Furthermore, the Android system optimized with Ark compiler is close to Apple’ iOS terminology. However, an open source HarmonyOS module built for embedded smart devices, OpenHarmony is not compatible with Android apps. 
An APK file is an archive that usually contains the following files and directories:
MANIFEST.MF: the Manifest file
- The certificate of the application.
CERT.SF: The list of resources and a SHA-1 digest of the corresponding lines in the MANIFEST.MF file; for example:
Signature-Version: 1.0 Created-By: 1.0 (Android) SHA1-Digest-Manifest: wxqnEAI0UA5nO5QJ8CGMwjkGGWE= ... Name: res/layout/exchange_component_back_bottom.xml SHA1-Digest: eACjMjESj7Zkf0cBFTZ0nqWrt7w= Name: res/drawable-hdpi/icon.png SHA1-Digest: DGEqylP8W0n0iV/ZzBx3MW0WGCA=
lib: the directory containing the compiled code that is platform dependent; the directory is split into more directories within it:
res: the directory containing resources not compiled into resources.arsc (see below).
assets: a directory containing applications assets, which can be retrieved by
AndroidManifest.xml: An additional Android manifest file, describing the name, version, access rights, referenced library files for the application. This file may be in Android binary XML that can be converted into human-readable plaintext XML with tools such as AXMLPrinter2, Apktool M, or Androguard.
classes.dex: The classes compiled in the dex file format executed by Android Runtime (or by Dalvik virtual machine used in Android 4.4 KitKat).
resources.arsc: a file containing precompiled resources, such as binary XML for example.
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Note: Historically the NDK supported ARMv5 (armeabi), and 32-bit and 64-bit MIPS, but support for these ABIs was removed in NDK r17.
- Dan, Albert (Sep 5, 2018). "Changelog r17". GitHub. Retrieved 2020-08-14.
Support for ARMv5 (armeabi), MIPS, and MIPS64 has been removed. Attempting to build any of these ABIs will result in an error.