DDR3 memory technology

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Figure 8: 4P memory architecture for AMD-based HP ProLiant G7 servers
HP ProLiant G7
AMD 4
-way architecture
CPU
CPU CPU CPU
HyperTransport Links
DDR3 DIMMs DDR3 DIMMs DDR3 DIMMs DDR3 DIMMs
The 4P AMD-based ProLiant G7 servers use a slightly different memory architecture than the 4P Intel-
based systems. Each processor has four memory controllers, each with a channel supporting either
two or three DDR3 DIMMs, depending on the system. The three DIMM memory channels are a “T”
electrically, with one DIMM installed at the center of the “T” and the other two DIMMs on the ends.
This design provides improved signal integrity by keeping the lengths of the electrical paths to the
DIMMs as close to the same length as reasonably possible. In order to help maintain this symmetry,
you install DIMMs on both ends of the “T” before installing the third DIMM in the center.
This architecture allows the memory subsystem to support DDR3 operating at 1333 MT/s when
memory channels are not fully populated. The absence of external memory buffering also results in
lower overall memory latency. Without buffering, however, the architecture only supports a maximum
of 48 DIMMs, or 1TB of system memory.
For ProLiant Gen8 servers, the AMD architecture does not change significantly. Without memory
buffering, these systems will support DDR3 memory operating at 1600 MT/s in smaller memory
configurations. With the availability of LRDIMMs capable of supporting three quad-rank DIMMs per
channel, the maximum memory footprint will increase to 1.5 Terabytes @667 MT/s.
Memory throughput with DDR3
Next, we turn our attention to memory throughput for systems using DDR3 memory.