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Subject: Re: Increasing memory. Will 64bit linux help?
Date: Wed, 17 Dec 2008 14:24:02 +0000 (UTC)
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"Ben Irv" <i.benjamin@ymail.com> wrote in message <gib18a$sqt$1@fred.mathworks.com>...
> "Gavrilo Bozovic" <gavrilo.bozovic@helbling.ch> wrote in message <giar6m$t3p$1@fred.mathworks.com>...
> > "Ben Irv" <i.benjamin@ymail.com> wrote in message <giaqnn$mok$1@fred.mathworks.com>...
> > 
> > Running a windows in a linux is a bad idea. If you switch to Linux, run Matlab in Linux.
> > 
> > Windows 32bits can access to 3Go of RAM, provided that you have 4 Go in your computer, and that you modify the boot.ini file (otherwise, 2Go are reserved for windows). By the way, I guess you mean RAM when speaking about virtual memory. Virtual memory is not RAM, check wikipedia for more info. You can allocate to Matalb virtually any amount of virtual memory, but it will be disk storage used as RAM, which will be VERY slow.
> > 
> > Now what exactly is your problem? Often, people have simulations that require a lot of computational power, although not a lot of RAM. In this situation, augmenting the RAM won't diminish the calculation time. Large amounts of RAM are especially required when running calculation on very large matrixes.
> 
> Hi Gavrilo
> 
> Thanks for the information. I think you are probably right that it is a bad idea to try and run windows apps on linux. 
> 
> I was talking about virtual memory. 32 bit operating systems limit the virtual memory for any application to 2 Gb which can my increased to 3 Gb. But unfortunatley that limit includes both RAM and page file memory. (see http://www.mathworks.com/support/tech-notes/1100/1107.html#_Toc170182654) " In particular, the processor limit is the maximum amount of virtual memory a single process (application) can address.  On 32-bit systems this is the most important factor limiting data set size" 
> 
> The reason I need so much RAM is that I'm working in image processing with (unfortunately) 512 by 512 by 150 arrays that are doubles.
> 
> regards
> Ben

Okay, I didn't know that the virtual memory was also limited.

However, I'm still wondering why you require so much RAM. I'm personnally doing FEM simulations with over 1M degrees of freedom. This gives a jacobian matrix of 1M x 1M. I have 8 Go of RAM (on a 64bits windows XP), but the only time I used them all was when I tested the system to know what it would be capable of. I don't recall exactly the number of degrees of freedom I had to put to require virtual memory in addition to RAM, but it was huge.

I'm not saying here that your code isn't optimized, I may be missing something! ;)

Anyway, if you're on windows 32 bits now, I'd say the most straightforward to do would be to switch to windows 64 bits. It doesn't have these memory limitations, and you'll have less work to do than to change to a Linux platform.