28 Sun Fire X4170, X4270, and X4275 Servers Installation Guide • December 2009
DIMM Population Rules
The DIMM population rules for the Sun Fire X4170, X4270, and X4275 Servers are as
follows:
1. Do not populate any DIMM sockets next to an empty CPU socket. Each processor
contains a separate memory controller.
2. Each CPU can support a maximum of:
■ Nine dual-rank (DR) or single-rank (SR) DIMMs; or
■ Six quad-rank (QR) DIMMs with two per memory channel; or
■ Three QR DIMMs with one per channel and three DR or SR DIMMs.
3. Populate DIMMs by location according to the following rules:
■ Populate the DIMM slots for each memory channel that are the farthest from
the CPU first.
For example, populate D8/D5/D2 first; then D7/D4/D1 second; and finally,
D6/D3/D0. See
FIGURE 2-3.
■ Populate QR DIMMs first, followed by SR or DR DIMMs.
■ Populate QR DIMMs in blue sockets (D8/D5/D2) first then white sockets
(D7/D4/D1). See
FIGURE 2-3.
Note that QR DIMMs are supported only in white sockets if adjacent blue
socket contains a QR DIMM.
■ Populate QR, SR, or DR DIMMs in sets of three for each CPU, one per
memory channel. See
FIGURE 2-3.
4. For maximum performance, apply the following rules:
■ The best performance is ensured by preserving symmetry. For example: adding
3x of same kind of DIMMs, one per memory channel; and, if the server has two
CPUs, ensuring that both CPUs have the same size of DIMMs populated in the
same manner.
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