What is Native Image Generator (Ngen.exe)?

The Native Image Generator (Ngen.exe) is a powerful tool that generates a platform-specific binary image for the current operating system. This image is then stored in a dedicated cache on the local computer, known as the native image cache. The primary purpose of generating native images is to enhance the performance of assemblies by allowing them to load and execute more efficiently. Instead of dynamically generating code and data structures during runtime, the assembly can retrieve them directly from the native image cache, resulting in faster execution.

Native Image Generator


One significant advantage of using native images is the improved startup time of applications. Once the native image is generated, the .NET runtime can utilize it to run the code, eliminating the need to fetch it from the hard disk. As a result, when an assembly is executed, the Common Language Runtime (CLR) first searches for a matching native image based on various factors such as the processor architecture and version compatibility. If a suitable native image is found, it is employed for executing the code, bypassing the slower JIT compilation and type-safety verification processes associated with MSIL code.

ngen install MyApp.exe

The above command generates a native image for MyApp.exe, located in the current directory, and installs the image in the native image cache.

ngen install c:\project\MyApp.exe

The above command generates a native image for MyApp.exe with the specified path.

ngen uninstall c:\project\MyDll.dll /ExeConfig:c:\project\MyApp.exe

The above command uninstalls the MyDll.dll from the previous example.


The use of native images can greatly enhance the performance of .NET applications, particularly in terms of startup time. By using pre-compiled binary images, the runtime can expedite the execution process, leading to a more responsive and efficient application experience.