How come there is no 64bit build of R for Windows?

Question

How come R does not have a 64bit windows pre-built binaries?

Answer 1

Update

Current versions of R for Windows (since R 2.11) do come with 64-bit executables.

In the past no suitable free compiler was available. Quoting from the old R-on-Windows FAQ (taken from the sources and hence with texinfo markup):

To build a 64-bit version on 64-bit Windows you will need a suitable compiler, and experiments with the Mingw64 port of @code{binutils} and @code{gcc} have failed to produce a working version on R. You are of course welcome to try a commercial compiler@footnote{such as those from Intel and PGI: there is no Fortran compiler in the Microsoft set, but @code{f2c} could be used.}, and pre-compiled versions using such compilers are available from R redistributors.

REvolution Computing had a Windows 64 bit version in their commercial / enterprise product before the official R gained 64-bit support.