[R] Memory available to 32-bit R app on 64-bit machine

[Prof Brian Ripley]

On Tue, 27 Jun 2006, roger bos wrote:

> I want to get a 64-bit machine/OS system so I can put 16Gb of RAM in it.  As
> first I assumed that I would have to use the 64-bit version of R to make use
> of the 16Gb of RAM, which would mean that I would use the Linux version of
> R.  But I have heard many posters say they run the 32-bit version of R on a
> 64-bit machine/OS.

Yes, and the address-space limits on 32-bit applications still apply: it 
is done for speed.

> So my questions, in Windows 64-bit, how much memory
> would be available to the 32-bit R binary?  Is it 4Gb (because its a 32-bit
> application) or 16Gb (because its being run on a 64-bit OS)?

2Gb, as it is a rather limited 32-bit subsystem of a 64-bit OS.  See the 
reference in the rw-FAQ Q2.9 or ?"Memory-limits".

No 32-bit OS gives 4Gb address space to an application: most manage about 
3Gb.  See ?"Memory-limits" (which is tailored to the OS you are running).

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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
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