IBM 7945G2U, Installation And User Manual

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Table 7. Maximum memory installation using ranked DIMMs
Number of DIMMs DIMM type DIMM size Total memory
12 Single-rank UDIMMs 2 GB 24 GB
12 Dual-rank UDIMMs 4 GB 48 GB
18 Single-rank RDIMMs 2 GB 36 GB
18 Dual-rank RDIMMs 2 GB 36 GB
18 Dual-rank RDIMMs 4 GB 72 GB
18 Dual-rank RDIMMs 8 GB 144 GB
12 Quad-rank RDIMMs 16 GB 192 GB
v
The RDIMM options that are available for the server are 2 GB, 4 GB, 8 GB, and
16 GB. The server supports a minimum of 2 GB and a maximum of 192 GB of
system memory using RDIMMs.
For 32-bit operating systems only: Some memory is reserved for various
system resources and is unavailable to the operating system. The amount of
memory that is reserved for system resources depends on the operating system,
the configuration of the server, and the configured PCI devices.
v
The UDIMM options that are available for the server are 2 GB and 4 GB. The
server supports a minimum of 2 GB and a maximum of 48 GB of system memory
using UDIMMs.
Note: The amount of usable memory is reduced depending on the system
configuration. A certain amount of memory must be reserved for system
resources. To view the total amount of installed memory and the amount of
configured memory, run the Setup utility. For additional information, see
Chapter 3, “Configuring the server,” on page 143.
v
A minimum of one DIMM must be installed for each microprocessor. For
example, you must install a minimum of two DIMMs if the server has two
microprocessors installed. However, to improve system performance, install a
minimum of three DIMMs for each microprocessor.
v DIMMs in the same system must be the same type (UDIMM or RDIMM) to
ensure that the server will operate correctly.
v
When you install one quad-rank RDIMM in a channel, install it in the DIMM
connector furthest away from the microprocessor.
v
Do not install one quad-rank RDIMM in one channel and three RDIMMs in
another channel.
DIMM installation sequence
The server comes with a minimum of one 2 GB DIMM installed in slot 3. When you
install additional DIMMs, install them in the order shown in the following table to
optimize system performance. In non-mirroring mode, all three channels on the
memory interface for each microprocessor can be populated in any order and have
no matching requirements.When you install additional DIMMs, install them in the
order shown in Table 8 on page 107, to maintain performance.
Important: If you have configured the server to use memory mirroring, do not use
the order in Table 8 on page 107; go to “Memory mirroring” on page 107 and use
the installation order shown there.
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System x3650 M3 Types 4255, 7945, and 7949: Installation and User’s Guide