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Cisco UCS C420 Server Installation and Service Guide
OL-27640-01
Chapter 3 Maintaining the Server
Installing or Replacing Server Components
DIMM Population Rules
Observe the following guidelines when installing or replacing DIMMs (see Figure 3-13):
• The minimum configuration is one DIMM installed in any of CPU1’s blue sockets (A1, B1, C1, D1).
• When populating a channel, fill the blue socket first, and then fill the black sockets (1, 2, 3).
• The server supports one, two, or three DIMMs per channel for single- or dual-rank DIMMs.
• The server supports only one or two quad-rank registered DIMMs (RDIMMs) per channel. The
server supports one, two, or three quad-rank load-reduced DIMMs (LRDIMMs) per channel.
• The server supports RDIMMs or LRDIMMs. Do not mix RDIMMs and LRDIMMs in a server.
• Unregistered DIMMs (UDIMMs) and non-ECC DIMMs are not supported.
• For memory mirroring population rules, see Memory Mirroring Mode, page 3-25.
• There is no requirement to install DIMMs evenly across all CPUs. However, for optimal
performance, you should populate sockets in the order that is shown in Table 3-4 for two-CPU
systems or Table 3-5 for four-CPU systems.
Table 3-4 DIMM Population for Two-CPU System Optimum Performance
# of DIMMs
Installed CPU
DIMM
Socket Color
First: 1 CPU1 C1 Blue
2CPU2E1Blue
3CPU1D1Blue
4CPU2F1Blue
5CPU1B1Blue
6CPU2H1Blue
7CPU1A1Blue
8CPU2G1Blue
9CPU1C2Black
10 CPU2 E2 Black
11 CPU1 D2 Black
12 CPU2 F2 Black
13 CPU1 B2 Black
14 CPU2 H2 Black
15 CPU1 A2 Black
16 CPU2 G2 Black
17 CPU1 C3 Black
18 CPU2 E3 Black
19 CPU1 D3 Black
20 CPU2 F3 Black
21 CPU1 B3 Black
22 CPU2 H3 Black
23 CPU1 A3 Black
Last: 24 CPU2 G3 Black
