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Basics of DDR3 memory technology

Fig: DDR3

DDR3, the third-generation of DDR SDRAM technology, makes improvements in bandwidth and power consumption over DDR2. Additional improvements in DDR3 yield up to 70% power savings versus DDR2 at the same speed, and 100% higher bandwidth over DDR2.

DDR3 Memory Technology
DDR3 DIMMs use the same 240-pin connector as DDR2 DIMMs, but the notch key is in a different position.
To increase performance and reduce power consumption, DDR3 incorporates several key enhancements:

•  Standard DDR3 DIMMs operate at 1.5V, compared to 1.8V for DDR-2 DIMMs. DDR3 Low Voltage DIMMs operate at 1.35V. For HP ProLiant Gen8 servers, the majority of new DDR3 DIMMs are Low Voltage. These HP SmartMemory DIMMs enable the same performance as standard 1.5V DIMMs while using up to 20% less power.
• An 8-bit prefetch buffer stores more data before it is needed than the 4-bit buffer for DDR2
• Fly-by topology (for the commands, addresses, control signals, and clocks) improves signal integrity by reducing the number of stubs and their length. The improved signal integrity, combined with “write leveling” technology, enables DDR3 to operate at significant faster transfer rates than previous memory generations.
• A thermal sensor integrated on the DIMM module signals the chipset to reduce memory traffic to the DIMM if its temperature exceeds a programmable critical trip point.

DDR3 Speeds
The DDR3 specification originally defined data rates of up to 1600 Mega transfers per second (MT/s), more than twice the rate of the fastest DDR2 memory speed (Table 2). ProLiant G6 and G7 servers support a maximum DDR3 DIMM speed of 1333 MT/s. ProLiant Gen8 servers use the new 1600 MT/s DDR3 DIMMs as well as 1333 MT/s DIMMs.
The DDR3 specification has been extended to define additional memory speeds of 1866 MT/s and 2166 MT/s. ProLiant Gen8 servers currently support memory speeds up to 1600 MT/s. HP engineers have designed the ProLiant Gen8 platform architecture to run at memory speeds up to 1866 MT/s once processor chipsets and DIMMs that support this speed are available.

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