Re: [R] Speed up R

From: Mike Prager <mike.prager_at_noaa.gov>
Date: Wed, 20 Jun 2007 16:21:18 -0400

"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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