[mechy]

Hi All
I have compared the prices of two CPUs Xeon E5-2643 v4(1300EUR)and Intel Core i7 6800K (~360 EUR)
.
Both CPUs has the same core and frequency. But their prices are very different.
I would be so grateful if anyone can tell me why these CPU prices is very different
Also, if I use these CPU for CFD simulations (assume the other computer parts is identical), I get the same performance or not.

• Intel Core i7 6800K, S 2011-3, Broadwell-E, Six Core, 12 Thead, 3.4GHz Clock, 3.8GHz Turbo, 15MB, 28 Lane, 140W, Retail
• Intel Xeon E5-2643 v4, S 2011-3, Broadwell-EP, 6 Core, 3.4GHz, 3.7GHz Turbo, 20MB, 40 Lane, 9.6GT/s QPI, 135W, OEM

This high difference cost between the Xeon and core i7 also exist between following CPUs

• Intel Core i7 6900K, S 2011-3, Broadwell-E, 8 Core, 16 Thead, 3.2GHz Clock, 4GHz Turbo, 20MB, 40 Lane, 140W, CPU, Retail (895EUR)
• Intel Xeon E5-2667 v4, S 2011-3, Broadwell-EP, 8 Core, 3.2GHz, 3.6GHz Turbo, 25MB, 40 Lane, 9.6GT/s QPI, 135W, OEM (1700EUR)

Best Regards

[flotus1]

You mixed up the prices. The Xeon processors are the expensive ones.

The differences (E5-2643 v4 vs. i7 6800K) are: ECC-Support, 2S scalability and 40 vs 28 PCIe lanes for the Xeon. The I7 on the other hand has an unlocked multiplier and (inofficially) can use memory faster than DDR4-2400.
The E5-1xxx Xeons (no scalability) are the more suitable counterparts for the I7 CPUs. The v4 versions of these CPUs should become available within a few weeks. But they will still be more expensive than the I7 CPUs.

Using ONE of these CPUs for CFD simulations, you will get about the same level of performance. Unless you overclock CPU and memory with the I7.

[mechy]

Dear Alex
Thanks so much for your answer.
I am not expert in computer hardware science.
can you explain more about the advantages of Xeon CPU (ECC-Support, 2S scalability and 40 vs 28 PCIe lanes) with respect to I7 ?
can these advantages of Xeon cause to increase the CFD performance ?

Best Regards

[flotus1]

These features will not affect performance for a typical CFD workload. Lets break it down...

ECC support: Error correctng code (ECC) memory can detect and correct single-bit memory errors. This feature is useful for server applications and other stuff where system stability is the single most important property of the system.
For a CFD workstation with a single processor and a "typical" amount of RAM (lets say not more than 128GB) it is not necessary.
For ECC to work properly you need a CPU and a motherboard with a chipset that support ECC. And quite obviously ECC-memory which is a bit more expensive than normal memory. If you buy a Xeon procesor anyway, get ECC memory. It won't do any harm.

2S scalability: The ability to use two CPUs in a shared memory system, thus two CPUs on one motherboard. Great for larger workstations as it effectively allows you to get twice the performance without having to deal with distributed memory issues. But be aware that you pay a premium price for CPUs with this capability. If your workstation only has one CPU and you need no more than 10 cores, these CPUs are the wrong choice. You can easily see the scalability of Intels Xeon CPU: it is the first digit in the four-digit model number. e.g. Xeon E5-1650v4 -> only one CPU. Xeon E5-2630v4 -> up to two CPUs. Xeon E5-4669v3 -> up to 4 CPUs. Xeon E7-8890v4...you get the picture.
All non-Xeon Intel CPUs like the I7 are single-socket only. Long story short, if you plan for a CFD workstation with a single CPU get an I7 or a Xeon E5-1xxx.

PCIe-lanes: They are used for communication between stuff like the graphics card and the CPU. Any modern GPU uses 16 of these lanes. So unless you are planning to use more than two graphics cards (feeding one graphics card with only 8 lanes usually isn't much of a bottleneck) the 28 lanes provided by the I7-5820k/6800k are enough.
It gets a little more complicated with the latest peripherals like USB 3.1 and PCIe-SSDs. In modern platforms like Intels Skylake for consumers the chipset provides the additional lanes required to connect these devices. However, since the "Enthusiast" platform (X99, the one used for I7-5820k/6800k) did not really catch up with recent hardware developments the chipsets fail to provide these additional lanes. Thus the lanes from the CPU are used. This can be problematic with only 28 lanes in total when 24 of them are already used by two graphics cards.
Again to wrap things up: with only one graphics card in your workstation you don't need to worry if 28 PCIe lanes are enough. They are.

So in conclusion: For a typical CFD workstation with only one CPU and the price/performance ratio in mind, Intels "enthusiast" I7 CPUs are the best option.

[mechy]

Dear Alex
Thanks so much for your answer.
I have another question
what is the difference between the OEM and Retail properties of CPUs ?

Best Regards
Yasser

[flotus1]

To be honest I am not familiar with the concept of OEM and retail when it comes to CPUs. Where did you find this? Or are you referring to the terms "tray" and "boxed".

[mechy]

in some online-markets they refer to OEM and retail box
it seems that as you told OEM=Tray and retail=box
by searching in the internet I have found that the box version includes fan, heat sink an more years warranty
am I right ?

Best Regards

[flotus1]

Exactly. If you are not a reseller, always buy "boxed" or "wof" (=without fan) CPUs. Even if you throw away the boxed cooler. You get the full warranty from Intel. But what is more important: "Tray" CPUs can be used and "negatively selected". Some people buy several CPUs at once and only keep the ones that perform best. The others are sent back and are then sold as "tray" versions.

[mechy]

In a workstation PC, how I can check the used CPU is the boxed or Tray ?

Thanks

[flotus1]

I don't know why that could be of interest. If you buy a complete workstation, the manufacturer has to provide some kind of warranty.
But to answer your question: you can't.

[hyugakojiro999]

Hi flotus1,

Could you please help me about deciding for a PC system?

-I'm not sure if 5820k or 6800k is better value. It seems the only big difference is 64GB / 128GB Ram capability and DDR4 2133mhz to 2400mhz Ram support.

-Another problem is Ram. Motherboard will support up to 3333mhz Ram (OC). If I use 3000mhz Ram, will it give any boost to system? Or will be downgraded by the CPU to 2133mhz?

-Cooling is problem either. You know the Fluent work... What kind of cooling system will i need?

-Lastly, does video card capacity effect solution speed or smth like that? For example, can i use a very low video card smth like 1gb and 128bit?


Here is my draft lists:

-INTEL i7-6800K 3.4 Ghz Socket 2011-v3 15MB 6 Cores

-MSI X99A SLI PLUS DDR4 3333MHz S+GL+16X 2011
-MSI N730-2GD3V2 GT730 2GB DDR3 128Bit HDMI 16x
-Samsung SSD 120Gb 850 Evo
-Seagate ST1000DM003 1TB 7200 NCQ SATA3 64MB
-4 sets of:CORSAIR 16 GB (2X 8GB) DDR4 2400 MHZ RAM CL14 Vengeance
-ZALMAN Z3 PLUS 600W MID TOWER ATX

----------------------------------

-Intel® Core™ i7-5820K Processor(15M Cache, up to 3.60 GHz)

-MSI X99A RAIDER DDR4 3333MHz S+GL+16X 2011
-HDD_SSD-2.5 SAMSUNG 120GB 850 EVO SERIES 540/52
-HDD_PC-3.5 1TB SEAGATE 7200RPM 64MB ST1000DM00
-ATX-ZALMAN Z3 PLUS 600W MID TOWER ATX KASA
-4 Sets: KINGSTON 2X8GB 16GB 2400Mh DDR4 C15
-MSI R7 360 OC GDDR5 2GB 128 Bit AMD Radeon DX12
-Noctua NH-D15

[flotus1]

To start with you might want to read this thread, it covers most of your questions (and some you did not ask but should know about):
http://www.cfd-online.com/Forums/har...modelling.html

I would go with the I7-6800k. It will draw less power and has better RAM compatibility when it comes to large quantities and high frequency.
Never mind that these CPUs officially support only up to DDR4-2400. Using XMP profiles or manual adjustment you can usually use much faster RAM. Be aware that beyond DDR4-2800, the CPU strap might be increased to 125MHz automatically. You might have to reduce the CPU multiplier to compensate for this.
Use the least amount of DIMMs possible to start with. In your case since you are aiming for 64GB total that would be 4*16GB. This increases system stability and RAM can be upgraded later if necessary.

Whatever you do, do not buy a Nvidia GT 730. It is old and slow. You will have trouble post-processing larger simulations with such a flimsy graphics card. The minimum should be a GTX 750TI with 2GB GDDR5.
Edit: And get an SSD with at least 240GB. Smaller models are just not worth the money and you will run out of disk space rather sooner than later.