[R] Amount of memory under different OS

[Prof Brian Ripley]

On Mon, 4 Apr 2005, bogdan romocea wrote:

> You need another OS. Standard/32-bit Windows (XP, 2000 etc) can't use
> more than 4 GB of RAM. Anyway, if you try to buy a box with 16 GB of
> RAM, the seller will probably warn you about Windows and recommend a
> suitable OS.

There _are_ versions of Windows 2000 and later which can support more than 
4Gb (and I hope if you buy a box with more memory you would be sold the 
appropriate version).  If you have a 32-bit address space you cannot have 
more than 4Gb of addresses, physical or virtual.  So some modern `32-bit' 
chips have segmented addressing: see e.g.

http://www.microsoft.com/whdc/system/platform/server/PAE/PAEmem.mspx

(where PAE is the scheme used on IA-32 aka ix86 chips).  AFAIK the story 
is the same for most IA-32 OSes: each process gets a 4Gb address space and 
(usually) 3Gb of that is user space.  R's memory usage will get cramped 
when the address space is tight: you probably do not want to be using 1Gb 
objects in a 3Gb address space (and if you need to, try R-2.1.0 beta).

The question did not mention R, and `very tough' is not at all explicit.

For large R tasks we have been recommending 64-bit OSes for quite a long 
time.  There are 64-bit versions of Windows for AMD64/EMD64T chips, but 
not versions of the compilers used to build R for Windows.  There are many 
users here of R under Linux (usually Fedora Core 3 or SuSE 9.x) on such 
chips.

> -----Original Message-----
> From: marvena at tin.it [mailto:marvena at tin.it]
> Sent: Saturday, April 02, 2005 12:48 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] Amount of memory under different OS
>
>
> I have a problem: I need to perform a very tough analysis, so I would 
> like to buy a new computer with about 16 GB of RAM. Is it possible to 
> use all this memory under Windows or have I to install other OS?


-- 
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