“Write once and run everywhere” is one of the most important promises made by Java technology. Java Virtual Machines running on different platforms support this promise. With Microsoft's .NET initiative also you can write a program in C, C++, C#, Visual Basic, Perl, and so on. Then you can convert the program (with Visual Studio .NET) into the Microsoft intermediate language (MSIL) binary code that can be executed on any Windows platform by a virtual machine called the Common Language Runtime (CLR).

Unfortunately, the problem has many sides, and no technology by itself can help in every direction. Again, this is about the right development process coupled with the right technologies. What are the factors, other than language and compatibility problems, that prevent us from writing once?

When we try to use an existing service or application with a new environment, we find out that it does not fit. When business requires change and we want to adapt an existing product to that change, we find that there are no adaptation mechanisms in place. We realize that the basic properties, methods, and operations of the application are too specific to and too tight with the existing environment. The product has to be redone, often from scratch.