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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
.
•
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
.
•
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.
