posted based on udemy video - Android OS Internals 😁

AOSP Project Folders

Android Source Code Directory	Description
art	ART(Android Runtime) operating environment. All the ART-related modules can be found here including dex compilers, JVM, dalvik VM, etc.
bionic	Android's custom C library. Bionic is Android's C library, math library, and dynamic linker.
bootable	Boot-related code. Contains Bootloader, OTA, recovery mechanism.
build	Build System. You can find envsetup.sh, common shell scripts and make, soong folders here. So these build systems are used to build the entrie AOSP Project.
compatibility	CDD (Compatibility Definition Document) documentation
cts	Android Compatibility Test Suite Standard. CTS tests ensure that you implementation is compatible with this latest AOSP build.
dalvik	Dalvik Virtual Machine-related code. Even though ART was introduced, android still uses the dex code. In this folder, there are modules supporting dex code generator and Dalvik eXchange.
developers	Developer Directory. Contains Demo and Sample Android Projects.
development	Application development related. Here you can find the development IDE like clion, eclipse, IntellJ under the ide folder. Lots of Sample implementation under samples folder. And many other folder to support app development like Python, vndk, etc.
device	Device-specific files and components. Here you can find the supporting configuration and driver files required for Development Boards like linaro hikey, ti, amlogic, etc.
external	External Open Source projects imported into the AOSP. This folder contains a lot of dependent project used by AOSP like Dagger2, exoplayer, flatbuffers, icu, jackson, rust and many many more. There are around 347 dependent modules in it as in AOSP 12.
dalbik	Dalbik Virtual Machine-related code. Even though ART was introduced, it still uses the dex code. In this folder, there are modules supporting dex code generator and Dalvik eXchange.
frameworks	Application framework, the core part of the Android system, written in Java and C++. Here you can find all the system service and core implementations of Android. As such it's where most APIs are defined: frameworks/base/core/java/android/app/ frameworks/base/cord/java/android/content/ frameworks/base/services/core/java contains most system services, and these directories typically have more granularity than core/java/, since they can be refactored without top layer API changes.
hardware	Mainly the code of the hardware abstraction layer and hardware support modules. Consists of the hal for audio, video, usb, tv, camera etc.
kernal	Contains kernel configs, prebuilts.
libcore	Consists of many core libraries related json, xmlparser, apache harmony etc.
libnativehelper	Dynamic library, the basis of the JNI library. It consists of helper functions to use with JNI.
ndk	NDK(Native Development Kit) related code to help developers embed C/C++ code in the application.
out	After the Build is complete, the code output is in this directory. You can find the generated images for the build here.
packages	Application package like Stock Android apps, providers, IMEs and many more.
pdk	Platform Development Kit. PDK (Platform Development Kit) is a reduced set of Android release provided to chipset vendors and OEMs before a new android platform is released. The goal of the PDK release is to help chipset vendors and OEMs to migrate to a new release. PDK release includes only necessary components for developing android HAL (Hardware Abstraction Layer). Note that the full android release is a superset of PDK release, and there is no separate PDK release to public as the full paltform release includes everything in PDK. Place-holder for tools and test codes for PDK. -Build: It is a place-holder for PDK build related stuffs. -apps: test apps
platform_testing	Platform test. Consists of platform test modules. https://source.android.com/compatibility/tests
prebuits	Consists of Prebuilt binaries. Includes toolchains like asuite, android emulator, Bazel etc.
sdk	Many SDK Tools sources can be found here. Instructions to build sdk for a specific build can be found here under docs.
system	It contains Low-level file system libraries, applications, and components. This is the "Embedded Linux" folder. Here you can find folders for selinux, logging, libhidl and many low level configurations.
test	Contains the test suites like csuite, catbox, vts(vendor test suite), mts(mainline test suite) etc.
toolchain	Toolchain files related to benchmark and pgoprofiles.
tools	Tool files like apksig, asuite, trade federation etc.