DDR3 FAQ

ddr3-faq

A new memory standard

What exactly is DDR3 memory?
DDR3 SDRAM or double-data-rate three synchronous dynamic random access memory is the name of the new DDR memory standard that has been developed as the successor to DDR2 SDRAM.

The memory comes with a promise of a power consumption reduction of 40% compared to current commercial DDR2 modules, due to DDR3′s 90 nm fabrication technology, allowing for lower operating currents and voltages (1.5 V, compared to DDR2′s 1.8 V or DDR’s 2.5 V). “Dual-gate” transistors will be used to reduce leakage of current.

DDR3′s prefetch buffer width is 8 bit, whereas DDR2′s is 4 bit, and DDR’s is 2 bit. The prefetch buffer is a memory cache located on modern RAM modules which stores data before it is actually needed. In addition to increased operation frequencies, decreased heat production, and increased latency, and increased bandwidth, the width of the prefetch buffer is increased with each successive standard of modern DDR SDRAM modules.

Theoretically, these modules could transfer data at the effective clockrate of 800-1600MHz (for a single clock bandwidth of 400-800MHz), compared to DDR2′s current range of 400-1066 MHz (200-533 MHz) or DDR’s range of 200-600 MHz (100-300 MHz). To date, such bandwidth requirements have been mainly on the graphics market, where fast transfer of information between framebuffers is required.

DDR3 DIMMS have 240 pins, the same number as DDR2; however, the DIMMS are physically incompatible, owing to a different key notch location.

Who defines DDR3?
The feature set of DDR3 is defined by the Joint Electronic Device Engineering Council or JEDEC in a process where all major players in the industry, such as Intel, AMD, Qimonda, Samsung, Micron, and OCZ have equal right to provide input and feedback. This process ensures fairness and a balance between the needs of each of the contributors.

Is DDR3 memory the same as used in the Xbox 360?
The GDDR3 memory, with a similar name but an entirely dissimilar technology, has been in use for several years in high-end graphic cards such as ones from NVIDIA or ATI Technologies, and as main system memory on the Xbox 360. It is sometimes incorrectly referred to as “DDR3″.

Is DDR3 supported by all brand name suppliers in the computer industry?
All major memory foundries support and develop DDR3, and all major platform enablers have or are in the process of adopting the new technology.

Why was DDR2 so short-lived compared to DDR and what will happen to DDR3 in that respect?
The life span of the first generation of DDR was unusually long, primarily because of some fragmentation among the different chipset and CPU manufacturers that will be remembered as “the Rambus War”. Because of this, DDR was pushed to more than twice its originally intended speed, and DDR2 had to follow in the same path. As a result, we saw DDR scaling up over 5 years to 500MHz and now we see DDR2 1066 where originally DDR2-533 was meant to be the ceiling in merely 3 years, which is the usually life cycle of a memory architecture. However, the current speed is approximately where the DDR2 architecture hits its built-in limitations with respect to core speed and bus topology and it is a time for another changing of the guards. DDR3 will most likely maintain the same life cycle of approximately 3 years until the industry moves on to DDR4.

Is DDR3 faster than DDR2?
DDR3 prefetches 8 bits per core clock cycle, this allows to run the I/Os at 8x the core clock frequency. In other words, DDR3 is eight times faster than an SDRAM part running at the same core frequency. As a consequence, DDR3 modules will start at 800MHz and will scale well beyond 1600MHz.

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