Multicore JIT is a great new feature in .NET Framework 4.5. Multicore JIT parallelizes the some of the JIT compilations that happens on the start of the application, Historically .NET FW has used the Ngen Native Image Generator for parallelization. It works particularly well where this Ngen is installed. It has been with Silverlight 5 and ASP.NET. This post describes it’s features and how it works? Multicore JIT uses the parallelization to reduce the JIT compilation time during application startup. The fundamental problem with JIT compilation is , Jitting is normally a lazy operation, it Jits a method and do not what next method is for jitting. So the solution is it has to remember something from previous run which is all the jitting that happened and now you have a good idea of what we are going to JIT this time around and we know what to JIT before we need it.