Notes about the RNW file extension:
Incorrect file associations could be the result of underlying issues within your PC system. As such it is highly recommended to scan your PC for invalid registry entries, unused processes and other unfavourable system settings to identify slowdown issues.
The RNW file type is primarily associated with 'Sweave' by Friedrich Leisch. Sweave is a tool that allows you to embed the R code for complete data analyses in latex documents. Sweave source files are regular noweb files with some additional syntax that allows some additional control over the final output. Traditional noweb files have the extension .nw, which is also fine for Sweave files (and fully supported by the software). Additionally, Sweave currently recognizes files with extensions .rnw, .Rnw, .snw and .Snw to directly indicate a noweb file with Sweave extensions. Noweb is a simple literate-programming tool which allows one to combine program source code and the corresponding documentation into a single file.