The purpose of the directories under the Android SDK, and which are common under different systems.

There are many folders in the Android SDK directory, what are the main things?   1. Add-ons this contains additional libraries, such as Google Maps, of course, if you install the ophone SDK, there will be some class libraries inside.   2. Docs This is the Android SDK API Reference document, all the APIs can be found here.   3. market_licensing as a copyright protection component of Android Market, it can be used to anti-piracy in the general release of paid applications to the electronic marketplace. 4. Platforms is a real file for each Platform SDK, which will be based on the API level of the SDK version, here on Android 2.2来 said, entered after a android-8 folder, android-8 into the after IS Android 2.2 The main file of the SDK, where Ant is the ant compilation script, data holds some system resources, images is the emulator image file, skins is the skin of the Android emulator, templates is the default template created by the project,  Android.jar is the main framework file for this release, and the Tools directory contains important compilation tools such as AAPT, Aidl, reverse Debugging Tools Dexdump, and compile-script dx. 5. Platform-tools holds some common tools, such as ADB, and AAPT, Aidl, DX, and so on, Android123 hints that there are some duplicates in the Tools folder here and in the platforms directory, mainly from Android  2.3 Beginning these tools are divided into generic. 6. Samples is the default example project that comes with Android SDK, Apidemos is highly recommended for beginners to run learning, for SQLite database operation can see Notepad This example, for game development Snake,  Lunarlander is a good example, for Android theme development home is the theme of the Android M5 era design principles. 7. Tools, as Tools folder under the SDK root, contains important tools such as DDMS for launching Android debugging tools such as logcat, screen, and file Manager, While Draw9patch is the tool to draw a scalable PNG image on the Android platform, Sqlite3 can manipulate the SQLite database on a PC, while Monkeyrunner is a good stress test application that simulates user random keys, Mksdcard is the simulator SD image creation tool, emulator is the Android emulator main program, but from Android 1.5, you need to enter the appropriate parameters to start the simulator, TraceView as an important debugging tool on the Android platform.  8. Usb_driver, as its name implies, is the driver of Google's official Android platform, such as Nexus One, Nexus S, and some old-model-driven support such as HTC Dream, HTC Magic and Motorola's droid.is ANDROIDSDK under Windows and Linux generic? 
The SDK is not all of the data are platform-differentiated, some of the data is common, and the common part of the data is the largest in the entire SDK,
Let's talk about what directories a complete SDK contains, and where Android-sdk-windows is the Sdkhome directory (android-sdk-linux)
Linux directory is a little different, that is Sdkmanager, win under this software in the root directory of the Sdkhome directory, the AVD software is also in the root directory,
In Linux, Sdkmanager and Avdmanager (not actually called the two names but an executable file called Android) are in the Tools folder of the Sdkhome directory,
Sdkhome Below are:
Add-ons Universal
Build-tools not Universal
Docs General
Extras Universal
Platforms Universal
Platform-tools not Universal
Samples Universal
Sources Universal
System-images Universal
Temp generic (This is a temporary folder for Sdkmanager update data, may not exist, no need to do so)
Tools Not Universal
Above is a complete directory of the SDK included, of course, does not guarantee that Android future updates will add a new directory

The purpose of the directories under the Android SDK, and which are common under different systems.