Backward compatibility means that an application
that is developed for a particular version of a platform will also run on the
later versions of that platform. The .NET Framework tries to maximize the
backward compatibility: Source code written for one version of the .NET
Framework should compile on the later versions of the .NET Framework, and the
binaries that run on one version of the .NET Framework should behave identically
on the later versions of the .NET Framework.
.NET Framework 4.5 and its point releases are
backward-compatible with apps that were built with earlier versions of the .NET
Framework. In other words, apps and components built with the previous versions
will work without modification on the .NET Framework 4.5 as well. However, by
default, apps do run on the version of the common language runtime for which
they were developed, so you may have to provide a configuration file to enable
your app to run on the .NET Framework 4.5.
? Note that the .NET Framework 4.5 is not
supported on Windows XP.
? .net 4.5 comes automatically with windows 8
? .net 3.5 sp1 comes automatically with windows
7 sp1