In March 2009, Intel® Corporation launched its new server processors, code-named "Nehalem-EP", or Xeon® 5500 series processors.
This new generation of processors incorporates a DDR3 memory controller to support new, high-performance DDR3 memory modules.
The new platforms can support two different types of memory modules:
Registered DIMMs or Unbuffered ECC DIMMs, depending upon the desired memory capacity of the servers.
Unbuffered ECC DIMMs (or ECC UDIMMs) are intended for lower-end servers and workstations requiring no more than 24GB of memory using 2GB modules; Registered DIMMs are intended for mid-range and high-end servers which could require more than 24GB of memory with the higher reliability offered by Registered DIMMs. PDF
Intel XEON 5500 Nehalem FAQs
What types of memory do the new Xeon 5500 series processor (code-named Nehalem-EP) based platforms use?
The new platforms use DDR3 Registered ECC DIMMs or DDR3 Unbuffered ECC DIMMs up to 1333MHz and feature Triple Channel architecture for enhanced performance.
Kingston® offers “K3” kits of three memory modules that are identical for use on Triple Channel platforms.
Please ensure that K3 kits are installed in the three matching memory sockets on the new platforms.
For 4- and 8-socket low-cost platforms, Kingston offers single DIMMs to install with the K3 kits, or K4 kits of 4.
Can these two memory types be mixed?
No. A single platform must use either all Registered DIMMs or all Unbuffered ECC DIMMs.
Registered DIMMs are abbreviated as RDIMMs and Unbuffered ECC DIMMs as ECC UDIMMs.
Why would I use Unbuffered ECC DIMMs?
They cost less.
ECC UDIMMs are intended for entry-level servers and workstations where memory capacity is less critical.
ECC UDIMMs cost significantly less than RDIMMs up to 2GB, while 4GB ECC UDIMMs cost substantially more than 4GB RDIMMs due to the expensive DRAMs they require.
Why would I use Registered DIMMs?
They offer higher memory capacity.
Registered DIMMs are the best choice for mid-range and high-end platforms where memory capacity is critical.
RDIMMs are currently available from Kingston in capacities ranging from 1GB to 16GB.
How do I know which speed memory to buy?
Kingston offers one speed – the fastest – for Single- and Dual-Rank DDR3 modules at 1333MHz and 1066MHz for Quad-Rank modules.
Kingston memory automatically clocks down, based on which model processor is installed and how many K3 kits are installed per processor.
Why is my installed memory running at a slower speed when I have my system fully populated?
Intel’s Xeon 5500 series processors access memory using a parallel bus, which has limitations on how many memory “loads” (expressed in memory “Ranks”) it can support at a given time.
The more memory loads (K3 kits) installed means that the Xeon processor must slow memory down in order to compensate.
Memory speed may also be limited according to the Xeon model that is installed.
Check the processor model for memory speed rules to know how to achieve the best performance.
How can I reduce memory power consumption and generated heat?
Server power consumption and heat can be reduced by using as few modules as possible for a given capacity and using only 4GB or 8GB modules.
When available, server and workstation manufacturers offer Low Power modules, as does Kingston.
These Low Power modules will drive down the operating costs of servers and further reduce heat generated by requiring less power.
What are the 4-memory socket and 8-memory socket platforms?
These are Triple Channel-based platforms with an extra memory socket for use when greater memory capacity is needed.
This fourth memory socket is limited to operate in Single Channel mode when it is used.
Kingston offers K3 and K4 kits, as well as single modules for these platforms.
What is the “thermal sensor”?
Kingston’s DDR3 RDIMMs and DDR3 ECC UDIMMs incorporate a thermal sensor that is used to monitor the memory module’s temperature and allow the platform to better manage thermal conditions for more reliable operation.