\HeaderA{Memory-limits}{Memory Limits in R}{Memory.Rdash.limits}
\keyword{environment}{Memory-limits}
\begin{Description}\relax
\R{} holds objects it is using in memory.  This help file documents the
current design limitations on large objects: these differ between
32-bit and 64-bit builds of \R.
\end{Description}
\begin{Details}\relax
\R{} holds all objects in memory, and there are limits based on the
amount of memory that can be used by all objects:
\Itemize{
\item There may be limits on the size of the heap and the number of
cons cells allowed -- see \code{\LinkA{Memory}{Memory}} -- but these are
usually not imposed.
\item There is a limit on the address space of a single process such
as the \R{} executable.  This is system-specific, but 32-bit OSes
imposes a limit of no more than 4Gb: it is often 3Gb or less.
\item The environment may impose limitations on the resources
available to a single process -- see the OS/shell's help on commands such
as \code{limit} or \code{ulimit}.
}
Error messages beginning \code{cannot allocate vector of size}
indicate a failure to obtain memory, either because the size exceeded
the address-space limit for a process or, more likely, because the
system was unable to provide the memory.  Note that on a 32-bit OS
there may well be enough free memory available, but not a large enough
contiguous block of address space into which to map it.

There are also limits on individual objects.  On all versions of \R,
the maximum length (number of elements) of a vector is
\eqn{2^{31} - 1 \approx 2\thinspace 10^9}{2^31 - 1 ~ 2*10^9}, as
lengths are stored as signed integers.  In addition, the storage space
cannot exceed the address limit, and if you try to exceed that limit,
the error message begins \code{cannot allocate vector of length}.
The number of characters in a character string is in theory only
limited by the address space.
\end{Details}
\begin{SeeAlso}\relax
\code{\LinkA{object.size}{object.size}(a)} for the (approximate) size of \R{} object
\code{a}.
\end{SeeAlso}

