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1.35V vs 1.5V RDIMMs performance

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October 8, 2013 11:04:43 AM

Hi,

Building a new system, Xeon based and researching the net about the types of RAM I could use. I stumbled upon an article that states

quote:"Users who have high performance needs of DDR3 RDIMMs must be aware of, when you populate more than one PC3L-low voltage RDIMM per memory channel, a DDR3-1333 speed DIMM will clock down to DDR3-1066 memory speed. However, the 1.5V standard voltage DDR3 counterpart will run at the full DDR3-1333 memory speed with 2 RDIMMs per channel in Xeon 5650 or higher based servers. Performance users are better off selecting standard 1.5V RDIMMs when populating up to 12 RDIMMs in a 2-way server." end of quote.

Here is the link to the full article which dates Dec 11th 2011
http://www.dataram.com/blog/?p=102

The company looks like a very reputable source of info.

The memory I need is DDR3-1600/1866Mhz RDIMMs

What do you guys think about that? I couldn't find the same info anywhere else but there are more experts here that could answer the question.

More about : 35v rdimms performance

a c 163 } Memory
October 8, 2013 11:16:11 AM

I understood.

The quote basically says this.

If you install only 1 PC3L-low voltage RDIMM with a RAM stick DDR3-1333, this will run at those speeds. BUT if you install more than one DDR3-1333 this will automatically down-clock to DDR3-1066,

What memory type you should use? That depends of how many RDIMM slot do you plan to use, according to that quote and assuming that you want install more than one RDIMM, you should go with DDR3-1333 at 1.5V
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October 8, 2013 1:59:33 PM

saint19 said:
I understood.

The quote basically says this.

If you install only 1 PC3L-low voltage RDIMM with a RAM stick DDR3-1333, this will run at those speeds. BUT if you install more than one DDR3-1333 this will automatically down-clock to DDR3-1066,

What memory type you should use? That depends of how many RDIMM slot do you plan to use, according to that quote and assuming that you want install more than one RDIMM, you should go with DDR3-1333 at 1.5V


Thanks for posting,
The reason I asked the question was that in all the 1.35V vs 1.5V RAM discussions no one pointed out about the difference in performance stated in the article. Also presuming that the article is two years old I thought that there could be other opinions or changes to the characteristics of the memory. Also that could be true only regarding RDIMMs and not the rest of the memory types.

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a c 163 } Memory
October 8, 2013 2:06:13 PM

The difference is 1333 to 1066. Two years old article would be a problem, but personally I would contact to manufacturer (if you can) and ask again.

I don't think that at this time that limit continues, but is better be sure before buy something.
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