[R] Speed up R

[Matthew Keller]

So Mike, let me ask you a question. If R runs out of RAM, does it
begin to use virtual RAM, and hence begin to swap from the hard drive?
If so, I could see how a faster hard drive would speed R up when you
don't have enough RAM...



On 6/20/07, Mike Prager <mike.prager at noaa.gov> wrote:
> "Matthew Keller" <mckellercran at gmail.com> wrote:
>
> > Robert,
> ...
> > As for Mike Prager's point about the type of hard drive being
> > important, I'm not sure this is right (someone correct me if I'm
> > misunderstanding). R stores and accesses objects through RAM - they
> > aren't stored and accessed on the hard drive except when reading and
> > writing. So hard drive type probably won't make much difference to
> > speed in R.
>
> In my experience, it makes a substantial difference if any
> swapping to disk is going on. That will happen if, e.g., other
> processes or Windows itself need RAM. Though R keeps the data in
> RAM, under Windows, non-SCSI disk I/O puts a noticeable load on
> the CPU. As SCSI controllers have CPUs of their own, they
> offload much of that work from the system CPU.
>
> I have compared dual-processor computers with equal RAM, one
> with a SCSI subsystem and one with fast (7200 RPM) ATA disks and
> slightly faster CPUs.  One was my work machine, one my home. The
> difference was not subtle.  For another example, think of how
> slow laptops seem when multitasking, compared to a good
> workstation. It is usually the poor disk subsystem that's the
> bottleneck, not the CPU.
>
> Mike
>
> --
> Mike Prager, NOAA, Beaufort, NC
> * Opinions expressed are personal and not represented otherwise.
> * Any use of tradenames does not constitute a NOAA endorsement.
>
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-- 
Matthew C Keller
Postdoctoral Fellow
Virginia Institute for Psychiatric and Behavioral Genetics