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.
What are the new features of DDR3 that make it faster?
First of all, as mentioned, the core outputs 8 bits per cycle and I/O pin, and that effectively allows increasing of the data frequency to 8x that of the core clock. Second, there are novel Dynamic On-Die Termination schemes that are calibrated during the initialization of the memory to assure optimal interaction between the memory and the rest of the system. Third, where DDR2 was only partially terminated, DDR3 is fully terminated including addresses and commands.
Is there a physical difference between DDR2 and DDR3 modules?
Yes, DDR3 modules have their key in a different location, making it impossible to insert them into a DDR2 motherboard. There is a reason for that in part DDR3 runs at lower voltage and further uses slightly different signals. Also, the power and ground planes are physically separated and grouped in central and peripheral planes to help insulating them from each other.
Does DDR3 use more or less power than DDR2?
The nominal supply voltage of DDR3 is lower than that of DDR2, that is 1.5V compared to 1.8V, respectively and that results in lower power per clock cycle. However, since DDR3 will run twice as fast as DDR2, the average power consumption will be 38% higher. This means that there will be 38% more heat as well that needs to be managed and, coincidentally, DDR3 will use SPD entries to define the presence or absence of heatspreaders.
Will there be registered DDR3 modules for servers?
It is very likely that the entire scenario of broadcasting addresses and commands to every chip will become the limiting factor for the DDR3 performance if performance is defined as frequency. It is a simple equation in which the power that is used to drive addresses and commands across the bus will cause some serious drains and bounces above 1600 MHz and the only way to avoid this is to use registers as intermediate chips between the controller and the chips on the modules.
How many DIMMs are supported in a DDR3 system?>
The original idea was that with increasing the chip density to 1 Gbit or 2 Gbit, two memory slots would suffice to have enough system memory. This is essentially still true, especially in 32-bit operating systems, but people like to upgrade without being orced to discard their original hardware – in this case memory. Therefore, most motherboards will feature four DDR3 DIMM slots and that will give the end-user the flexibility to configure their systems any way they want.
Can you list out DDR3 features in a bulleted format?
Sure can…
DDR3 SDRAM Components:
- Introduction of asynchronous RESET pin
- Support of system level flight time compensation
- On-DIMM Mirror friendly DRAM ballout
- Introduction of CWL (CAS Write Latency) per speed bin
- On-die IO calibration engine
- READ and WRITE calibration
DDR3 Modules:
- Fly-by command/address/control bus with On-DIMM termination
- High precision calibration resistors
Advantages compared to DDR2
- Higher bandwidth (up to 1600 MHz)
- Performance increase at low power
- Longer battery life in laptops
- Enhanced low power features and thermal design
Disadvantages compared to DDR2
- Commonly higher CAS Latency
- Lower MFIBS per Quad Cycle