While the Dell PowerEdge M420 uses the Intel Xeon E5-2400 architecture, the unique form factor limits the memory capacity compared to its half-height brother, the PowerEdge M520, so it today’s post, I’ll be discussing the memory architecture of the M420.

The Intel Xeon E5-2400 memory architecture is very similar to what you may be familar with on the Intel Xeon 5600 series – 3 memory channels per CPU.  Whereas the typical server running the Intel Xeon E5-2400 server would have 6 DIMMs per CPU, or 12 DIMMs total, the PowerEdge M420 is restricted to 6 memory DIMMs, or 3 DIMMs per CPU, as seen in the cross section of the M420.

The M420 is capable of a maximum of 96GB of memory using 16GB DIMMs.  Once the 32GB DIMMs become available (later this year) the maximum memory will increase to 192GB.

Memory Capacity

The PowerEdge M420 offers memory speeds of 1600 and 1333 MHz, but it depends on DIMM capability as well as the maximum CPU speed (see below.)  There are 2 voltages that are supported: a standard DIMM voltage of 1.5v which support speeds up to 1600, and a Low Voltage  DIMM (1.35 V) which supports speeds up to 1333 MHz.

The available DIMM sizes in the 1333 MHz speed are:

• 2GB RDIMM, 1333 MHz, Low Volt, Single Rank, x8
• 4GB RDIMM, 1333 MHz, Low Volt, Single Rank, x4
• 4GB RDIMM, 1333 MHz, Low Volt, Dual Rank, x8
• 8GB RDIMM, 1333 MHz, Low Volt, Dual Rank, x4
• 16GB RDIMM, 1333 MHz, Low Volt, Dual Rank, x4

The available DIMM sizes in the 1600 MHz speed are:

• 4GB RDIMM, 1600 MHz, Standard Volt, Dual Rank, x8
• 8GB RDIMM, 1600 MHz, Standard Volt, Dual Rank, x4
• 16GB RDIMM, 1600 MHz, Standard Volt, Dual Rank, x4

It is important to understand in order to run memory at 1600 MHz, you will need to insure that you choose an Intel Xeon E5-2400 CPU that runs at 1600 MHz.  Currently, the CPUs that run at 1600 MHz are:

•  Intel® Xeon® E5-2470 2.30GHz
• Intel® Xeon® E5-2450 2.10GHz
•  Intel® Xeon® E5-2450L 1.80GHz

Memory Rules

As with any server, there are some memory rules to be aware of with the PowerEdge M420 server:

• If DIMMs of different speeds are mixed, all channels across all CPUs operate at the slowest DIMM’s common frequency.
• Only RDIMMs are supported, no UDIMMs or LRDIMMs.
• DIMMs must be installed in each channel starting with the DIMM farthest from the processor.
• DIMMs should be installed with largest rank count to smallest.  (Example: if a Dual Rank (DR)  is mixed with Single Rank (SR) DIMMs, DR’s should be placed in the lowest DIMM slots then the SR DIMMs.)

Additional Resources

Finally, I’ll leave you with some places to find additional information about the PowerEdge M420.

• Dell 12G Memory Solution Tool – http://www.poweredgecpumemory.com/
• PowerEdge M420 Home Page – http://dell.to/PowerEdgeM420
• Dell PowerEdge M420 Systems Owner’s Manual (PDF) – View
• Dell PowerEdge M420 QR Tag videos – http://www.youtube.com/playlist?list=PL46414AA1BAA82B1A

Kevin Houston is the founder and Editor-in-Chief of BladesMadeSimple.com.  He has over 15 years of experience in the x86 server marketplace.  Since 1997 Kevin has worked at several resellers in the Atlanta area, and has a vast array of competitive x86 server knowledge and certifications as well as an in-depth understanding of VMware and Citrix virtualization.  Kevin works for Dell as a Server Specialist covering the Global 500 East market.