5137ch02.fm
Draft Document for Review October 14, 2014 10:19 am
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IBM Power Systems E870 and E880 Technical Overview and Introduction
provide memory expansion up to 125%, depending on the workload type and its memory
usage. As an example, a server with 256 GB of RAM physically installed can effectively be
expanded over 512 GB of RAM. This approach can enhance virtualization and server
consolidation by allowing a partition to do more work with the same physical amount of
memory or allowing a server to run more partitions and do more work with the same physical
amount of memory.
2.3.1 Custom DIMM
Custom DIMMs (CDIMMs) are innovative memory DIMMs that house industry-standard
DRAM memory chips and a set of components that allow for higher bandwidth, lower latency
communications and increased availability. These components include:
Memory Scheduler
Memory Management (RAS Decisions & Energy Management)
Memory Buffer
By adopting this architecture for the memory DIMMs, several decisions and processes
regarding memory optimizations are run internally into the CDIMM. This saves bandwidth and
allows for faster processor-to-memory communications. This also allows for a more robust
RAS. For more information, see Chapter 4, “Reliability, availability, and serviceability” on
page 145.
The CDIMMs exists in two different form factors, a 152 SDRAM design named the Tall
CDIMM and an 80 SDRAM design named the Short CDIMM. Each design will be comprised
of multiple 4 GB SDRAM devices depending on its total capacity. The CDIMMs slots for the
Power E870 and Power E880 are tall CDIMMs slots. A filler is added to the short CDIMM
allowing it to properly latch into the same physical location of a tall CDIMM and allows for
proper airflow and ease of handling. Tall CDIMMs slots allow for larger DIMM sizes and the
adoption of future technologies more seamlessly.
