double cpu performance?

[Epiclol86]

After watching the latest LTT, i found myself with more questions than answers about double cpu rigs:

 

how does the performance scale up? Can you use them as one cpu gigahertz wise, doubling the processing power, for example does 2x q6600 (quad core 2.4 ghz)= quad core 4.8 or does it just become an eight core  2.4 ghz cpu? i am inclined in believing more in the second option, but...

 

also is there problems with it like when you have double gpu's, like programs not compatible with it or something?

 

is there one cpu that is the "first" cpu, like it uses up the first and then adds the second when needed, or does your mobo consider it like one cpu?

 

is your motherboard able to use the full performance of both cpu's, or does it reduce the performance across the board, even slightly?

 

When you OC (if you even can) does it oc both at the same time, or do you OC and OV each seperately? and if you oc separatly, what happens to RAM frequency?

 

 

I know, it's a lot of questions, and i'm still going all over the internet, as a brave google explorer should, to find answers, but they are quite difficult to find since double cpu boards are quite unusual!

 

i hope you can answer some of these, and if you do, thank you!

[ZetZet]

8 core 2.4 ghz cpu and still not quite as fast as an actual 8 core 2.4 ghz cpu.

[multifrag]

From my knowledge only xeons can be put into multi cpu motherboard. @ZetZet it is difficult to compare different cpu as architecture could and most probably would if one would have 2x4 and the other one would be 1x8. One this I can tell is that they scale 100% which should be expected.

[SaladFingers]

From my own experience with a board that uses two X5365s, no, you won't be getting full performance everywhere. It is actually why I won't bother with such a setup again until multithreading etc becomes more popular. Some games will essentially only use one of the CPUs (or from what i mostly noticed, use both CPUs but both will be capped at about 50% usage). To answer one of your questions, no it won't be like "when cpu 1 maxes out start using cpu 2" etc. It will be mostly spread across all cores on both the CPUs, even if a program really just uses two cores for example, you will see your used cores jumping around in both CPUs most of the time.

 

In the end, is it a good choice for gaming? Perhaps. If you can get them cheap and have patience that games are going to support more cores in the future (which I was hoping about few years ago, not hoping much anymore). Is it a good choice for regular use? Again it depends. If you can get them at the same price as, say an i5, then yes they are worth it.

 

What will mostly benefit from such a setup is rendering and VMing, or generally a server machine that you throw things at it from several terminals at the same time.

 

PS: When talking about dual-CPU configs you are probably looking into Xeons, which can't really OC much at all, so don't bother about it. The motherboards made for two CPUs can handle them just fine, nothing will slow down because of it.