Ngen

The Native Image Generator is a utility that allows you to create CLR images in native code from assemblies on the CIL code for the runtime environment and install it in the assembly cache of the local computer. Due to this, the efficiency of managed applications is increased: instead of the JIT compilation, the finished assembly is loaded on the native code.

Benefits:

• Reduces application loading time since no JIT compilation is required.
• reduces the time of the first launch of functions, since JIT compilation is not required.
• improves memory usage, since a JIT compiler is not required.
• received dlls can be used simultaneously by many processes. (sharing between processes)
• compilation takes place for a specific processor used in the system.

Disadvantages:

• Limitations on the use of the Assembly.LoadFrom method
• Native image does not replace the original dll, but is stored separately. Therefore, more disk space is used.
• Unsynchronized NGen files. When a new version of the assembly appears, you must update the image in the local cache.
• Since the native image and the source assembly have different addresses for functions, when calling methods that are in the native image, the operation of modifying the base address is added.

Application:

• If the dll uses many processes or it is used from different domains. Native image will enable the simultaneous use of the library by many processes.
• If you need to speed up the launch of the application and reduce the memory used.
• Application to large programs gives a greater effect than application to small programs.
• For programs with a long runtime, the effect is very small (since JIT compilation is performed only once - on the first call. Next, the compiled version is used. And with each new call, the total difference will decrease.)

All .NET frameworks during installation create images in a native image.