DDR3 Server Memory: LV 1.35V or Standard 1.5V–What Shall I Choose?

~written by Nelson Rodriguez, Dataram Memory Blog Team Member

DDR3 Low voltage 1.35V RDIMMs are becoming mainstream in today’s x86 servers featuring Intel’s Xeon 5600 series CPUs—also known as “Westmere”.    Standard DDR3 DIMMs run at 1.5V.  DDR3 memory technology has evolved since it became mainstream in 2008, with a series of die shrinks each resulting in lower power consumption.

By “going green”, let’s compare power consumption in a 96GB capacity server.  First generation 50nm DRAMs would draw about 65W of power.  A die shrink to 40nm lowered power consumption to under 43W, for about a 34% reduction.  By again shrinking the die to 30nm technology AND lowering the voltage to 1.35V, this results in an additional 21% power reduction, down to under 34W.  These comparisons are from our friends at Samsung, the world’s largest maker of DRAMs.  As you calculate the power savings over an entire datacenter with large numbers of servers, the savings become substantial.  The advantages of LV (PC3L-) RDIMMs are obvious for servers, so what’s the catch?

Performance users deploy servers with one item in mind—extract the maximum application performance possible, and use IT infrastructure as a competitive advantage.  This is especially true with our customers involved in the financial services industry.  Securities trading in particular are most concerned about low-latency operation and want the fastest possible CPU and memory speeds.  After all, on Wall Street, “TIME IS MONEY”.

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.

Which is best—maximum power or maximum performance?   As the customer, you decide based on your needs.  Dataram has the full complement of memory options to enable you to go any way you choose.  Dataram’s team of memory specialists and our industry-leading customer support group will help you choose!

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