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Intro to CoreRT

Native (AOT) compilation is a great scenario addition to .NET Core apps on Windows, OS X and Linux. We've seen significant startup and throughput benefits of native compilation for Windows UWP apps, using .NET Native. Today, many native apps and tools benefit from being compiled by a C++ compiler, and not as much by being written in C++. CoreRT brings much of the performance and all of the deployment benefits of native compilation, while retaining your ability to write in your favorite .NET programming language.


CoreRT is a native toolchain that compiles CIL byte code to machine code (e.g. X64 instructions). By default, CoreRT uses RyuJIT as an ahead-of-time (AOT) compiler, the same one that CoreCLR uses as a just-in-time (JIT) compiler. CoreRT can also be used with other compilers, such as LLILC, and IL to CPP (an IL to textual C++ compiler we have built as a reference prototype). .NET Native uses CoreRT in conjunction with the UTC compiler to provide native compilation for UWP apps.

CoreRT is a refactored and layered .Net Core runtime. The base is a small native execution engine that provides services such as garbage collection(GC). This is the same GC used in CoreCLR. Many other parts of the traditional .NET runtime, such as the type system, are implemented in C#. We've always wanted to implement runtime functionality in C#. We now have the infrastructure to do that. In addition, library implementations that were built deep into CoreCLR, have also been cleanly refactored and implemented as C# libraries.

For more information about the architecture, see .


CoreRT offers great benefits that are critical for many apps.

  • The native compiler generates a SINGLE FILE, including the app, managed dependencies and CoreRT.
  • Native compiled apps startup faster since they execute already compiled code. They don't need to generate machine code at runtime nor load a JIT compiler.
  • Native compiled apps can use an optimizing compiler, resulting in faster throughput from higher quality code (C++ compiler optimizations). Both the LLILLC and IL to CPP compilers rely on optimizing compilers.

These benefits open up some new scenarios for .NET developers

  • Copy a single file executable from one machine and run on another (of the same kind) without installing a .NET runtime.
  • Create and run a docker image that contains a single file executable (e.g. one file in addition to Ubuntu 14.04).


To start, we are targeting native executables (AKA "console apps"). Over time, we'll extend that to include ASP.NET Core apps. You can continue to use CoreCLR for your .NET Core apps. It remains a great option if native compilation isn't critical for your needs. CoreCLR will also provide a superior debugging experience until we add debugging support to CoreRT.