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
