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Memory Subsystem Architecture
The HP ProLiant DL580 G7 provides a 2TB memory footprint and supports up to 64 DDR3 RDIMMs. Each of the
server’s four processors receives 16 RDIMM sockets in two easily serviceable memory cartridges. The DL580 G7
supports 2, 4, 8, 16, and 32GB RDIMMs.
The server incorporates four processors. Each processor contains two memory controllers as shown above in Figure
2. Each memory controller has two Scalable Memory Interface (SMI) links operating in lockstep. Each SMI link
connects to a scalable memory buffer (SMB). The SMB converts SMI to DDR3 and expands memory capacity of the
system. Each SMB supports two DDR3 channels, and each DDR3 channel can support up to two DIMMs for eight
DIMMs per memory cartridge, 16 DIMMs per processor, and 64 DIMMs per system.
The new Intel Xeon Processor E7 and 7500 series memory architecture take advantage of multiple stages of memory
interleaving to reduce the perceived latency and increase throughput.
The scalable memory buffer (SMB) prevents the varying number of installed DIMMs (or their electrical loads) from
affecting the processor’s memory speed. The DL580 G7 runs all DIMMs at the highest possible speed that a given
processor supports.
The DDR3 memory speed is a function of the QPI bus speed supported by the processor. For example, processors
with a QPI speed of 6.4 GT/s run memory at 1066 MT/s. Processors with a QPI speed of 5.6 GT/s run memory at
978 MT/s, and processors with a QPI speed of 4.8 GT/s run memory at 800 MT/s.
Hemisphere mode
The memory architecture for the Intel Xeon Processor E7 utilizing the 7500 Series chipset design includes a high-
performance interleaving technology called Hemisphere mode (see Figure 3.) It combines the tracking resources of
both memory controllers within each processor to speed the movement of data along a cache-line by a process
called pipelining.
To utilize Hemisphere mode, the system processors must have identical DIMM populations behind both of their
memory controllers. To enable each processor to enter the Hemisphere mode, you must install and populate both
DIMM memory cartridges with identical memory capacities based on the DIMM installation guidelines.
Hemisphere mode produces the best overall performance for many applications. You can disable Hemisphere mode
if it produces lower performance for a particular application (for example, an RBSU option).
You can obtain better performance when populating all cartridges with either four or eight dual- or quad-rank
DIMMs. (The server does not support memory mirroring when it enables Hemisphere mode.)
Figure 3 below shows six examples of Hemisphere vs. Non-Hemisphere populations.