The other day I was working with a customer who was attempting to add memory modules to his Cisco C250 server.  Though he was using the correct combination of DIMMs, the server never seemed to recognize all of the added memory.  After placing a call to Cisco Support, we found that the answer to this riddle lies in understanding the wonderfully advanced Cisco UCS technology known as "Extended Memory Technology."

Cisco recognized that in virtual environments, the contstraints for virtual machine growth lies mostly in the ever increasing need for more memory, while processing power is typically not as much of a concern.  To address this problem, Cisco UCS systems have introduced Extended Memory Technology.  This very advanced server archecture allows for up to 384 GB of memory to be installed in each server while extending the life of traditional Intel 5500 and 5600 processors.  The ability to load so much memory into each physical host makes the Cisco UCS ideal for virtual deployments, especially VDI implementations.

Though there is a highly technical process for how the server is able to utilize such a large amount of memory without requiring an expensive CPU, the best way to describe the technology is by stating that the processors "see" each four module group as a single 16GB or 32GB DIMM.  This allows the CPUs to handle being fully populated (48 DIMMs) without dropping below the full speed of 1333MHz.

The trick, we discovered, is keeping the DIMMs together as they were originially packaged as Cisco ships each group as they should be installed in the server.  Thankfully, Cisco Support was able to pair the DIMMs back together, and the server is now working perfectly.

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