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Old   January 7, 2014, 16:25
Question Help Building Desktop - Have $2500 +- $500
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jwb
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Hi, I am building a new desktop specifically to run open foam. I would like to spend a good chunk of money on it and get a really powerful machine. Can anyone recommend parts (specifically a cpu and gpu) that I should look into??

Thanks!
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Old   January 8, 2014, 03:14
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I think you are starting to ask the question from the wrong end if you specifically want a powerful machine for OpenFOAM.


To start with, there's no point in having a tolerance of +- $500 .... If you want the most performance, just plonk down the maximum you can comfortably afford and get on with it.


Secondly, unless you are wanting to post-process particularly large models, spending much money on a very powerful GPU is not going to get you anything worthwhile right now.


Thirdly, don't start the parts selection process with the CPU. Rather try to figure out how you can get the maximum number of memory channels for your system. It may be that your budget just about stretches to a dual socket Xeon (lga 2011) or Opteron (socket G34) board, in which case you would be able to get 8 memory channels. Experience has shown that this is well worth getting, even if you have to compromise by buying near the bottom of the range Xeon or Opteron CPU's.
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Old   January 9, 2014, 21:23
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Quote:
Originally Posted by CapSizer View Post
I think you are starting to ask the question from the wrong end if you specifically want a powerful machine for OpenFOAM.


To start with, there's no point in having a tolerance of +- $500 .... If you want the most performance, just plonk down the maximum you can comfortably afford and get on with it.


Secondly, unless you are wanting to post-process particularly large models, spending much money on a very powerful GPU is not going to get you anything worthwhile right now.


Thirdly, don't start the parts selection process with the CPU. Rather try to figure out how you can get the maximum number of memory channels for your system. It may be that your budget just about stretches to a dual socket Xeon (lga 2011) or Opteron (socket G34) board, in which case you would be able to get 8 memory channels. Experience has shown that this is well worth getting, even if you have to compromise by buying near the bottom of the range Xeon or Opteron CPU's.
the first and second point of your reply are excellent.

the third... it depends on the problem size/type i think...
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Old   January 10, 2014, 01:31
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the first and second point of your reply are excellent.

the third... it depends on the problem size/type i think...
Not really. When we have tested this, for modern multi core cpu's, the performance in Cfd is almost entirely determined by the memory bandwidth. The cpu architecture and clockspeed come second. Therefore, maximising the number of memory channels makes a huge difference, for anything except the really small problems, and for those you don't need anything more than a laptop.

If I remember correctly, somebody posted a link here last month comparing a quad socket opteron system to a dual xeon. I think the two systems had the same number of cores, and cost roughly the same. The difference was dramatically in favour of the opteron, despite the entry level cpus used. The only (but important) downside was the much higher power usage of the quad. The point here is simply that 16 memory channels beat 8 easily. Likewise, 8 will easily beat 4 (dual vs single socket), provided that you can live with the power consumption.
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