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Cisco UCS C240 Server Installation and Service Guide
OL-25761-01
Chapter 3 Maintaining the Server
Installing or Replacing Server Components
• Any DIMM installed in a DIMM socket for which the CPU is absent is not recognized. In a
single-CPU configuration, populate the channels for CPU1 only.
• Although 1600 MHz DIMMs can be run in Power Saving Mode (low-voltage 1.35 V operation),
1600 MHz operation is supported only when the DDR mode is set to Performance Mode (see
“Enabling Low-Voltage DIMM Operation.”) A 1600 MHz DIMM with DDR mode set to Power
Saving Mode operates at 1066 MHz.
• Observe the DIMM mixing rules shown in Table 3-4.
• Memory mirroring reduces the amount of memory available by 50% because only one of the two
populated channels provides data. When memory mirroring is enabled, DIMMs must be installed in
sets of 4, 6, 8, or 12 as described in Memory Mirroring, page 3-27.
• Note the following restrictions when using UDIMMs. Even though a UDIMM might be rated at
1600 MHz, actual operational speeds are slower because of the Intel implementation.
–
UDIMMs do not support 3 DIMMs per channel (3 DPC) configurations.
–
In Performance Mode (1.5 V operation), UDIMMs run at 1333 MHz in 1 DPC and 2 DPC
configurations.
–
In Power Saving Mode (1.35 V operation), UDIMMs run at 1066 MHz in 1 DPC and 2 DPC
configurations.
Enabling Low-Voltage DIMM Operation
You can enable low voltage (1.35 V) DIMM operation for all DIMMs in the server. There is a setting in
the BIOS Setup utility that you can use to change the DDR memory mode to Power Saving mode, as
described in the following procedure:
Step 1 Enter the BIOS setup utility by pressing the F2 key when prompted during bootup.
Table 3-4 DIMM Mixing Rules for C240 M3 Servers
DIMM Parameter DIMMs in the Same Channel DIMMs in the Same Bank
DIMM Capacity:
RDIMM = 4, 8, or 16 GB
LRDIMM = 32 GB
UDIMM = 4 GB
• You can mix different capacity
DIMMs in the same channel (for
example, A1, A2, A3).
• You cannot mix 32 GB LRDIMMs
with any RDIMM or UDIMM.
• You cannot mix 4 GB UDIMMs with
any RDIMM or LRDIMM.
• You can mix different capacity DIMMs
in the same bank. However, for optimal
performance DIMMs in the same bank
(for example, A1, B1, C1, D1) should
have the same capacity.
• You cannot mix 32 GB LRDIMMs with
any RDIMM or UDIMM.
• You cannot mix 4 GB UDIMMs with
any RDIMM or LRIMM.
DIMM Speed:
1866-, 1600-, or 1333-MHz
You can mix speeds, but DIMMs will run
at the speed of the slowest DIMMs/CPUs
installed in the channel.
You can mix speeds, but DIMMs will run at
the speed of the slowest DIMMs/CPUs
installed in the bank.
DIMM Type:
RDIMMs, LRDIMMs, or
UDIMMs
You cannot mix DIMM types in a channel. You cannot mix DIMM types in a bank.
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