JIT vs NGen - what is the difference?

Question

So when CLR runtime load a .NET assembly, it compiles it into machine native code. This process is called JITing. NGen is also the process of compiling .NET assembly into na

Answer 1

JIT is only done per-method; it doesn't JIT everything... Only the bits you need. Of course this has a small but measurable hit the first time into a method (plus generics etc). NGEN does this work up-front, but must be done on the same platform/architecture etc - essentially that machine. This also means adding it to the GAC etc, which may need higher access.

In many cases, JIT is fine, especially if the app is open for a long time (web servers, for example).