S is a programming language/environment for statistics and statistical graphics. S-Plus and R are implementations of S. This means that both products are built on the same basis; both execute the same functions (macros). Most common statistical functions progammed for S will run under R and vice-versa.

There are however a number of differences you should be aware of.

• In addition to typing in functions etc., S-Plus offers a highly developed graphical user interface (GUI), i.e. looks very different from R. R has a minimal graphical user interface. (There are however a number of developments underway to add a GUI to it).
• The standard data files for S and R are not compatible (there are however ways to transfer data easily).
• Graphical output differs quite often, as the products use different graphical engines and a different programming model, especially when it comes to programming complex graphics or/and include interaction.r
• Interfaces to other software, especially databases, are entirely different.

Conclusion: Most functions that do not use graphics or basic graphics run in both environments without any problem. Expect however problems when using more complex graphical tools. As this class addresses mainly visual tools, there will be many differences, not so much in what tools are available, but the functions will not be compatible, have different names and different implementations. As a rule these pages are concentrating on R; important differences with S are noted and some documents will be specific for S.