[R] R memory usage and size limits

[Tom Quarendon]

I have a general question about R's usage or memory and what limits 
exist on the size of datasets it can deal with.
My understanding was that all object in a session are held in memory. 
This implies that you're limited in the size of datasets that you can 
process by the amount of memory you've got access to (be it physical or 
paging). Is this true? Or does R store objects on disk and page them in 
as parts are needed in the way that SAS does?
Are there 64 bit versions of R that can therefore deal with much larger 
objects?

Many thanks.