Configuring and using DDR3 memory with HP ProLiant Gen8 Servers

Table 1. DDR3 memory speeds

DIMM Label JEDEC Name Data Transfer Rate Maximum DIMM Throughput

PC3 – 14900 DDR3-1866 1866 MT/s 14.9 GB/s

PC3 – 12800 DDR3-1600 1600 MT/s 12.8GB/s

PC3 – 10600 DDR3-1333 1333 MT/s 10.6 GB/s

PC3 – 8500 DDR3-1066 1066 MT/s 8.5 GB/s

PC3 – 6400 DDR3- 800 800 MT/s 6.4 GB/s

Basics of DIMMs

Before exploring the new technologies in DDR3 DIMMs for ProLiant Gen8 servers, let’s quickly review some of the basics

of DIMM technology.

DRAM technology

DIMMs are made up of DRAM chips that are grouped together. Each DRAM chip contains arrays of individual bit storage

locations. A DRAM chip with one billion storage locations is called 1 Gigabit (1Gb) technology. Note the lower case b in

Gb. Eight 1Gb chips ganged together will provide 1 GigaByte (1GB) of memory. Note the upper case B in GB.

DDR3 DIMMs are currently made up of 1Gb, 2Gb, and 4Gb DRAM chips. It is not possible to mix DRAM technologies on the

same DIMM. DDR3 does not support DIMMs made up of 512Mb DRAM chips.

A DRAM chip may have 4 data I/O signals or 8 data I/O signals. These are called x4 or x8, pronounced “by four” or “by

eight” respectively.

Ranks

A rank is a group of DRAM chips that are grouped together to provide 64 bits (8 Bytes) of data on the memory bus. All

chips in a rank are controlled simultaneously by the same Chip Select, Address and Command signals. DDR3 DIMMs are

available in single-, dual- and quad-ranks (1, 2, and 4 ranks respectively.)

Eight x8 DRAM chips or 16 x4 chips form a rank. DIMMs with 8 bits of Error Correction Code (ECC) use nine x8 chips and 18

x4 chips for each rank.

Speed

Speed refers to the frequency of the memory clock. The memory subsystem uses a different clock than the processor

cores, and the memory controllers use this clock to coordinate data transfers between the memory controller and the

DIMMs. The actual speed at which this clock operates in a particular server depends on five factors:

• Rated memory speed of the processor. Each Intel® Xeon® processor model supports a specific maximum memory

speed.

• Rated memory speed of the DIMM. DDR3 DIMMs can run at different speeds, often called frequencies. For ProLiant

Gen8 servers, we offer two native speeds of DDR3 memory: DDR3-1600 and DDR3-1333.

• Number of ranks on the DIMM. Each rank on a memory channel adds one electrical load. As the electrical loads

increase, the signal integrity degrades. To maintain the signal integrity the memory channel may run at a lower speed.

• Number of DIMMs populated. The number of DIMMs attached to a memory controller also affects the loading and

signal integrity of the controller’s circuits. In order to maintain signal integrity, the memory controller may operate

DIMMs at lower than their rated speed. In general, the more DIMMs that are populated, the lower the operational

speed for the DIMMs.

• BIOS settings. Enabling certain BIOS features can affect memory speed. For example, the ROM Based Setup Utility

(RBSU) in HP ProLiant servers includes a user-selectable setting to force memory to run at a slower speed than the

normally configured speed in order to save on power consumption. See the section on BIOS settings for details.