The new ASP.NET and the .NET Framework that it relies upon were rewritten to be open source and cross-platform. This work was called ASP.NET 5 while in development, but this has since been renamed to ASP.NET Core 1.0 to reflect that it's a new product with a stripped down set of features. Similarly, .NET Core 5 is now .NET Core 1.0, and Entity Framework 7 is now Entity Framework Core 1.0.
The web application framework that was called ASP.NET MVC has been merged into ASP.NET Core, although it's a package that can be added like any other dependency. The latest version of MVC is 6 and, along with Web API 2, this has been combined into a single product, called ASP.NET Core. MVC and Web API aren't normally referred to directly any more as they are simply NuGet packages that are used by ASP.NET Core. Not all features are available in the new Core frameworks yet, and the focus is on server-side web applications to start with.
All these different names can be perplexing, but naming things is hard. A variation of Phil Karlton's famous quote goes like this:
"There are only two hard things in Computer Science: cache invalidation, naming things, and off-by-one errors."
We've looked at naming here, and we'll get to caching later on in this book.
It can be a little confusing understanding how all of these versions fit together. This is best explained with a diagram like the following, which shows how the layers interact:
ASP.NET Core 1.0 can run against the existing .NET Framework 4.6 or the new .NET Core 1.0 framework. Similarly, .NET Core can run on Windows, Mac OS X, and Linux, but the old .NET only runs on Windows.
There is also the Mono framework, which has been omitted for clarity. This was a previous project that allowed .NET to run on multiple platforms. Mono was recently acquired by Microsoft, and it was open sourced (along with other Xamarin products). Therefore, you should be able to run ASP.NET Core using Mono on any supported operating system.
.NET Core focuses on web-application development and server-side frameworks. It is not as feature filled as the existing .NET Framework. If you write native-graphical desktop applications, perhaps using Windows Presentation Foundation (WPF), then you should stick with .NET 4.6.
As this book is mainly about web-application development, we will use the latest Core versions of all software. We will investigate the performance implications of various operating systems and architectures. This is particularly important if your deployment target is a computer, such as the Raspberry Pi, which uses a processor with an ARM architecture. It also has limited memory, which is important to consider when using a managed runtime that includes garbage collection, such as .NET.