[R] 32 vs 64 bit

[Prof Brian Ripley]

On Wed, 14 Dec 2005, Paul Gilbert wrote:

> I ran  R on an AMD Athlon 64 with a 32 bit Linux (by accident, I moved
> the hard disk from another machine). Now, after install 64 bit Linux and
> 64 bit R, I am finding some of my R tests are quite a bit slower, I
> think because memory demands cause a lot of swap. Does anyone know if
> extra memory usage would be mainly because of R itself, or is there a
> lot of extra memory demand because of the OS, windowing system, and
> other apps?

There's a definite effect from R itself.

I never run a machine without plenty of RAM for everyday tasks but if you 
did, that could have a bigger effect on a 64-bit OS as all the 
applications are larger.  (My 64-bit Opteron desktop has 2Gb, for example, 
whereas its 32-bit predecessor had 1Gb.)

This _is_ discussed in the R-admin manual (section 7 in R 2.2.0 in the 
version I just looked at).  You can run 32-bit R on 64-bit Linux if you 
want for speed (and I sometimes do): this too is discussed in the manual.

-- 
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)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595