as of R version 3:
It is now possible for 64-bit builds to allocate amounts of
memory limited only by the OS. It may be wise to use OS
facilities (e.g., ulimit in a bash shell, limit in csh), to set
limits on overall memory consumption of an R process,
particularly in a multi-user environment. A number of packages
need a limit of at least 4GB of virtual memory to load.
64-bit Windows builds of R are by default limited in memory usage
to the amount of RAM installed: this limit can be changed by
command-line option --max-mem-size or setting environment
variable R_MAX_MEM_SIZE.