Chapter 3. Product information 69
3.8 Memory
IBM DDR3 memory is compatibility tested and tuned for optimal System x performance and
throughput. IBM memory specifications are integrated into the light path diagnostics for
immediate system performance feedback and optimum system uptime. From a service and
support standpoint, IBM memory automatically assumes the IBM system warranty, and IBM
provides service and support worldwide.
As introduced in 2.4, “Memory” on page 30, the x3850 X6 and x3950 X6 support DDR3
memory operating at speeds up to 1600 MHz, 24 DIMMs per processor.
The x3850 X6 supports up to 96 DIMMs when all processors are installed.
The x3950 X6 supports up to 192 DIMMs when all processors are installed.
Each processor has four memory channels implemented using Scalable Memory Interface
generation 2 (SMI2) chips, and the server implements three DIMMs per channel. The
processor and the corresponding memory DIMM slots are located on the Compute Book.
The Intel Xeon E7-4800 v2 and 8800 v2 processors supports two memory modes,
Performance mode and RAS (or Lockstep) mode. These are described in 2.4.1, “Operational
modes” on page 31.
The following rules apply when selecting the memory configuration:
The server supports DDR3 memory RDIMMs and LRDIMMs.
Mixing different types of memory (RDIMMs and LRDIMMs) is not supported.
The maximum number of ranks per one DDR3 channel is 6 with RDIMMs or 24 with
LRDIMMs.
In RAS (Lockstep) mode, DIMMs must be installed in a pair.
Higher ranked DIMMs must be installed first.
A minimum of one DIMM must be installed in each Compute Book.
DIMMs in the server operate at the same speed, which is determined by the following
lowest value:
– Memory speed that is supported by the specific CPU
– Lowest of maximum operating speeds for selected memory configuration, depending
on rated speed, operating voltage, and quantity of DIMMs per channel, as shown
under the “Maximum operating speed” section in Table 3-6
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