Memory options for the IBM System x3650 M4 server – 16GB memory modules

For 16GB memory modules use at 1 DPC and 2 DPC

If the memory you need is going to require 1 DPC, or 2 DPC, you are better off buying the IBM RDIMMs.

http://www.redbooks.ibm.com/abstracts/tips0850.html
IBM System x3650 M4
IBM Redbooks Product Guide

The 1600MHz IBM 16GB RDIMMs (2-rank) will give you these speeds:

– 1 DPC at 1600MHz at 1.5V
– 2 DPC at 1600MHz at 1.5V
– 3 DPC at 1066MHz at 1.5V

The 1333MHz IBM 16GB RDIMMs (2-rank) will give you these speeds:

– 1 DPC at 1333MHz at 1.5V
– 2 DPC at 1333MHz at 1.5V
– 3 DPC at 1066MHz at 1.5V

If you use the low-voltage (1.35V) 1333MHz IBM 16GB RDIMMs (2-rank):

– 1 DPC at 1333MHz at 1.35V
– 2 DPC at 1333MHz at 1.35V
– 3 DPC not supported (at low voltage)

UPDATE: 05/31/2012 – corrected 1600MHz to 1333MHz

Therefore you do not get above 1066MHz at 3 DPC (a speed grade slowdown). This is caused by memory loading.

For 16GB memory modules use at 3 DPC (virtualization/cloud computing/data centers)

If you need to use 3 DPC (or are planning to upgrade to that later) – you can buy IBM 16GB HCDIMMs (Netlist HyperCloud):

– 3 DPC at 1333MHz at 1.5V

This is available on the high volume virtualization/data center servers:

– IBM System x3650 M4

http://www.netlist.com/news-and-events/2012-03-06/breaking-the-memory-bottleneck-with-hypercloud-hcdimm/
Breaking the Memory Bottleneck with HyperCloud DIMMs
March 6, 2012

http://www.netlist.com/news-and-events/2012-03-06/16gb-hcdimmm-ibm-x3650-m4/
16GB HCDIMM Available on IBM System x3650 M4 Servers
March 6, 2012

What about 16GB LRDIMM ?

16GB LRDIMMs are not an option because they underperform even the 16GB RDIMMs (2-rank):

– 16GB LRDIMMs can only do 3 DPC at 1066MHz (so why buy the LRDIMM)
– 16GB LRDIMMs have higher latency issues (so why buy the LRDIMM)

HP/Samsung at the IDF conference on LRDIMMs video (Inphi LRDIMM blog) have said they will not be pushing 16GB LRDIMMs (because it cannot compete against the 16GB RDIMM 2-rank). However they would push the 32GB LRDIMMs because they have some utility vs. 32GB RDIMMs (which will only be available in 4-rank for a few years because 8Gbit DRAM die won’t be available for a while if ever).