Since the inception of .NET Framework, there has always been one release at a time. Whenever a newer version was released, you could upgrade to the latest version or install multiple versions side by side. But there was always one single latest version.
Going forward, there are now two distinct versions: the full .NET Framework and the all-new .NET Core. While ASP.NET Core web applications can run on either one of them, you will decide which is more suitable for your needs. You can change the runtime during development or during release. Best of all, you can deploy the runtime alongside your released product, which allows multiple versions of .NET to be deployed to the same server.
The following screenshot illustrates how ASP.NET Core runs on both .NET Framework 4.6 and .NET Core 1.0:
Even with the release of .NET Core, there is still a place for the full .NET Framework. It will continue to be the framework of choice for rich Windows desktop applications, created with Windows Presentation Foundation (WPF) or Windows Forms. It will be one of two choices for ASP.NET Core developers.
For ASP.NET 4 developers, .NET Framework 4.6 will be an in-place replacement for .NET 4.x runtimes. This includes .NET 4, 4.5, 4.5.1, and 4.5.2. One good reason to upgrade to .NET 4.6 is the added benefit of new improvements such as better compilation and added language features.
The new .NET Core is a lightweight cross-platform subset of the full .NET Framework that makes its home on Windows, Linux, and OS X. It is expected to leap past the .NET Framework in new features that may make their way back to the .NET Framework.
It is worth noting that .NET Core is not an option for Windows desktop developers or ASP.NET 4 developers. In addition to supporting ASP.NET Core web applications with the CoreCLR runtime, .NET Core also includes the .NET native runtime, which is specifically used for Universal Windows Applications on Windows 10.
To recap, let's focus on the following benefits of running an ASP.NET Core web application on .NET Core, in addition to its cross-platform support:
Flexibility: With .NET Core, web applications can be deployed with a specific version of the .NET Core framework, which will allow you to deploy each application with only the version that it needs
Performance: With .NET Core, you'll enjoy performance benefits due to its lower memory footprint and faster start-up times
Whether you run ASP.NET on the full .NET Framework or the new .NET Core, you'll enjoy a modern application framework that eases you into cloud deployment and facilitates faster development with dynamic compilation.