Dimm Choices - HP DL370 - ProLiant - G6 Performance Introduction Manual

1333 Megatransfers per second (MT/s). While this is commonly referred to as having a speed of
1333 MHz, the maximum clock speed for the DIMMs is actually 667 MHz and the signal is double-
pumped to achieve the data rate of 1333 MT/s. DDR3-1333 DIMMs can operate at clock speeds of
667 MHz, 533 MHz and 400 MHz; with corresponding data rates of 1333, 1066, and 800 MT/s.
The three memory channels between the processor's integrated memory controller and the dedicated
DDR-3 memory provide a total bandwidth of 32 gigabytes per second.
Energy efficiency is improved over previous generations. HP DDR-3 DIMM modules incorporate an
integrated thermal sensor that signals the chipset to throttle memory traffic to the DIMM if its
temperature exceeds a programmable critical trip point. By using the data from these thermal sensors,
the ProLiant G6 servers can reduce fan speed and therefore reduce power consumption when
memory is idle. Some third-party DIMMs may not include this DIMM thermal sensor. The BIOS in
ProLiant G6 servers verifies the presence of the thermal DIMM sensor during POST. If the thermal
sensor is absent, a POST message will warn that the DIMM does not have a thermal sensor, and the
fans will be forced to run at higher speed (requiring more power).
Operating voltage for DDR-3 has been reduced. DDR-2 operates at 1.8V, while DDR-3 currently
operates at 1.5V, consuming less power than DDR-2 DIMMs at the same capacity and speed. DDR-3
DIMMs have the same number of pins and are the same physical size as DDR-2 DIMMs, but they are
electrically incompatible and have a different key notch location.

DIMM Choices

DDR-3 is available as both Unbuffered Dual In-line Memory Modules (UDIMMs) and Registered
(buffered) Dual In-line Memory Modules (RDIMMs). Both RDIMMs and UDIMMs support error
correcting code (ECC).
There are three types of DDR-3 available for ProLiant G6 servers:
• PC3-8500R (RDIMM, ECC compliant) —1066 or 800 MT/s data rate, depending on memory
configuration and processor installed.
• PC3-10600E (UDIMM, ECC compliant) —1333, 1066 or 800 MT/s data rate, depending on
memory configuration and processor installed
• PC3-10600R (RDIMM, ECC compliant) —1333, 1066 or 800 MT/s data rate, depending on
memory configuration and processor installed.
Administrators can configure ProLiant 300-series G6 servers using either RDIMMs or UDIMMs,
although RDIMM and UDIMM memory cannot be mixed within a single server. ProLiant 300-series
G6 servers have up to 18 DIMM slots, allowing larger memory capacities than with the platforms that
used DDR-2. ProLiant G6 servers optimize memory performance by operating DDR-3 memory at the
maximum rate possible, based on the memory configuration and processor installed.
When choosing memory configurations for 300-series G6 systems, the following guidelines should
prove helpful:
• UDIMM configurations are limited to a maximum of two UDIMMs per memory channel because the
memory controller must drive the address and command signals to each DRAM chip on a channel.
This results in a 24 GB maximum configuration in ProLiant 300-series G6 servers. Because they
require fewer components, UDIMMs are typically less expensive than RDIMMs.
• RDIMM configurations can provide larger memory capacity configuration because the memory
controller only drives the address and command signals to a single register chip, thereby reducing
the electrical load on the memory controller. Users requiring large memory footprints can install
three 8-GB RDIMMs per channel for a total of 144 GB.
• For smaller memory configurations, installing only one or two DIMMs per memory channel can
potentially increase memory performance. In many instances this allows administrators to clock the
memory channel at a higher data rate.
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