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32bit STAR on 64bit OS & CPU

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Old   April 25, 2005, 20:25
Default 32bit STAR on 64bit OS & CPU
  #1
Jihwan
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Hi there,

As you heard of it, MS is going to release their 64bit Window. Now, what happen do you think if I run 32bit STAR package on Window64 OS and AMD 64 bit CPU. Let's think about it in terms of two things. (1) first, speed up due to change of 64 bit OS & CPU is not anticipated. Only clock speed may speed up the calculation. (2) secondly, the main reason that I use AMD opteron is that 64 bit cpu can handle much larger problems larger than 10 million cells. Do you think the memory handling limitation get resolved if I run 32bit package on 64bit Window & 64bit CPU ?
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Old   April 25, 2005, 21:36
Default Re: 32bit STAR on 64bit OS & CPU
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Tom
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I use a LINUX system that has both 64 bit and 32 bit machines. The only way I get it to work is to build and decompose large models (>5 million cells) on the 64 bit machine and then run them on several 32 bit machines. However, for the LINUX machines, there is a 64 bit version of STAR.

Tom
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Old   April 25, 2005, 22:08
Default Re: 32bit STAR on 64bit OS & CPU
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stevef
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No - both the OS AND the application have to be 64bit enabled to get around the memory limitation. STAR is 64bit enabled on just about every Unix/Linux OS but not yet on Windows.
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Old   April 26, 2005, 04:46
Default Re: 32bit STAR on 64bit OS & CPU
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Jihwan
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Thank you for your comments, Tom and Stevef
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Old   April 26, 2005, 05:52
Default Re: 32bit STAR on 64bit OS & CPU
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Steve
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Further to the other points mentioned, don't try running a 32-bit executable on an Itanium2 chip (be it under HP-UX or Linux). It will run, but in an emulation mode, which is dog slow (as much as 4-6 times slower).

On the other hand, some 32-bit executables run FASTER than 64-bit ones on an Opteron chip.

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Old   May 23, 2005, 01:54
Default Re: 32bit STAR on 64bit OS & CPU
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Hubert Janocha
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Yes, thats my oberservation too. 32bit star-exectable runs very fast on Opterons, but when I compile on that opteron I have a speed up of about 0.9. I don't really understand the discussion about 64bit or 32bit. It is OK to have a local 64bit machine for meshing, but 32bit on a cluster for calculating is OK. Example: star needs about 1GB RAM for 1Mio cells (roughly). I have a cluster of 4 nodes with 2 CPU's and 2GBs on each node. Thats OK for 8.Mio cells, and I don't really need such great meshes. I am loosing time in generating such meshes.
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Old   May 23, 2005, 01:58
Default Re: 32bit STAR on 64bit OS & CPU
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Hubert Janocha
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Damm Microsoft. Please ask the StarCD-Holine. The same job is on the same machine with Linux at least about 1.3 faster than on Windows XP. Windows is not a really suitable platform for CFD in my opinion, but I know some engineers don't have the choice.
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