Six DIMMS slows memory? How much?

[Mark]

I'm looking to build systems using the GA-P55-UD6 motherboard.  At the bottom of the Memory Support List it states:

"Memory speed will drop when 6 DIMMs are all occupied"

Does anybody have information on why this is, or how much of a drop?
Can I simply buy faster memory? (I don't plan to overclock.)
I'm planning to use these as virtualization servers, so I'd like to have as much RAM as I can, although I'm unwilling to pay the huge price for 4GB modules.

Thanks for any help!

[runn3R]

Hi,

P55 chipset per it's spec supports only 4 DIMMs.

Because P55-UD6 has 6 DIMMs so DIMM2 and DIMM3 are shared in one channel. The same is with DIMM5 and DIMM6.

That’s why when all 6 slots are occupied, the memory speed will drop as follows:

1333 to 1066
1066 to 800.

[Mark]

I apologize for being so duff, but:   what can I do about it?

Can I buy faster memory?
If so, do I need to overclock the memory (on a GA-P55-UD6) or do I need to overclock the whole system?

Going to bones, if I go to 6 sticks what will happen to my system speed, and is there anything I can do to prevent the penalty?

Thanks again.

[runn3R]

What speed in MHz and amount in GB you want to have?

[Mark]

I want to run the i7-860 at 2.8 GHz, and I'd like to run 12 GB of memory at true 1333 MHz.

I'm looking at the GA-P55-UD6.  It seems the most significant advantage between the UD6 and the UD5 is the two extra memory slots.

But if using those slots slows the system...  it's hard to call it an advantage.

I think you are saying that I can overclock the memory to 1600 and get "real world" 1333 performance.  I don't mind paying a little extra for 1600 MHz memory.

Is it possible to overclock the memory independently of the CPU?

Mark

[runn3R]

The memory speed above 1333 (1600 and above) will be auto detected as 1333MHz.
If you would like to use 6 sticks of memory, these memory should be single sided.
Therefore, if you use 6 x 1600MHz sticks, the bios will auto detect them first as 1333 and then will downspeed to 1066 because 6 pcs are mounted.

It may be difficult to overclock from 1066 to 1333Mhz with 6 pcs memory and keep the system stable enough to use. But of course you may try doing it. You are free to ask other users here: http://forum.giga-byte.co.uk/index.php/board,43.0.html or in other forums, maybe somebody did it already...

The "official"   recommendation is to use 4GB sticks for this purpose, not 2GB, but I understand your concern about the cost.

P.S. UD6 is 24 phase power design, while UD5 is 12, see http://www.giga-byte.co.uk/FileList/WebPage/mb_090814_24/data/tech_090814_p55_u-24.htm

[Mark]

Thanks very much for all the insights.

I think I'll just restict myself to 8 GB of memory and not run so many Virtual Machines on each physical machine.

I admit I'm perplexed by the move to support six DIMMS if it causes a slowdown.  But maybe a 20% reduction in memory speed doesn't translate to a 20% reduction in performance.   (I bet there are articles out there!  Perhaps I should do my own research on this one.)

[runn3R]

(...) maybe a 20% reduction in memory speed doesn't translate to a 20% reduction in performance.   (I bet there are articles out there!  Perhaps I should do my own research on this one.)

Definitely it doesn't! There should be plenty of articles on web covering this.