Oct 31, 2008

DDR3 SDRAM


In electronic engineering, DDR3 SDRAM or double-data-rate three synchronous dynamic random access memory is a random access memory technology used for high speed storage of the working data of a computer or other digital electronic device.

DDR3 is part of the SDRAM family of technologies and is one of the many DRAM (dynamic random access memory) implementations. DDR3 SDRAM is an improvement over its predecessor, DDR2 SDRAM.

The primary benefit of DDR3 is the ability to transfer I/O data at eight times the speed of the memory cells it contains, thus enabling faster bus speeds and higher peak throughput than earlier memory technologies. However, there is no corresponding reduction in latency, which is therefore proportionally higher. In addition, the DDR3 standard allows for chip capacities of 512 megabits to 8 gigabits, effectively enabling a maximum memory module size of 16 gigabytes.

  





 Contents 



1 Overview

1.1 Latencies

2 Extensions

3 Specification standards

3.1 Chips and modules

4 References

5 See also

6 External links





Overview



DDR3 memory promises a power consumption reduction of 30% compared to current commercial DDR2 modules due to DDR3's 1.5 V supply voltage, compared to DDR2's 1.8 V or DDR's 2.5 V. The 1.5 V supply voltage works well with the 90 nanometer fabrication technology used for most DDR3 chips. Some manufacturers further propose using "dual-gate" transistors to reduce leakage of current.[1]

According to JEDEC[2] the maximum recommended voltage is 1.575 volts and should be considered the absolute maximum when memory stability is the foremost consideration, such as in servers or other mission critical devices. In addition, JEDEC states that memory modules must withstand up to 1.975 volts before incurring permanent damage, although they are not required to function correctly at that level.

The main benefit of DDR3 comes from the higher bandwidth made possible by DDR3's 8 bit deep prefetch buffer, in contrast to DDR2's 4 bit prefetch buffer or DDR's 2 bit buffer.

DDR3 modules can transfer data at the effective clock rate of 800–1600 MHz using both rising and falling edges of a 400–800 MHz I/O clock. In comparison, DDR2's current range of effective data transfer rate is 400–800 MHz using a 200–400 MHz I/O clock, and DDR's range is 200–400 MHz based on a 100–200 MHz I/O clock. To date, the graphics card market has been the driver of such bandwidth requirements, where fast data transfer between framebuffers is required.

DDR3 prototypes were announced in early 2005. Products in the form of motherboards are appearing on the market as of mid-2007 based on Intel's P35 "Bearlake" chipset and memory DIMMs at speeds up to DDR3-1600 (PC3-12800).[4] AMD's roadmap indicates their own adoption of DDR3 in 2008.

DDR3 DIMMs have 240 pins, the same number as DDR2, and are the same size, but are electrically incompatible and have a different key notch location.[5] DDR3 SO-DIMMs have 204 pins.







Latencies



The typical latency for a DDR2 JEDEC standard was 5-5-5-15. The JEDEC standard latencies for the newer DDR3 memory are 7-7-7-15. One thing to be aware of, however, is that while these are the standards, manufacturing processes tend to improve with time. Eventually, DDR3 modules will likely be able to run at lower latencies than the JEDEC specifications. It is possible to find DDR2 memory that is faster than the standard 5-5-5-15 speeds, but it will take time for DDR3 to fall below the JEDEC latencies.

DDR3 latencies are numerically higher because the clock cycles by which they are measured are shorter; the actual time interval is generally equal to or lower than DDR2 latencies.

GDDR3 memory, having a similar name but being from an entirely dissimilar technology, has been in use for high-end graphic cards by companies such as NVIDIA and ATI Technologies. GDDR3 has sometimes been incorrectly referred to as "DDR3".





Extensions



Intel Corporation officially introduced the eXtended Memory Profile (XMP) Specification on March 23rd, 2007 to enable enthusiast performance extensions to the traditional JEDEC SPD specifications for DDR3 SDRAM.



Specification standards



Chips and modules








Features



DDR3 SDRAM Components:

Introduction of asynchronous RESET pin



Support of system level flight time compensation



On-DIMM mirror friendly DRAM pin out



Introduction of CWL (CAS Write Latency) per speed bin



On-die I/O calibration engine



READ and WRITE calibration



DDR3 Modules:

Fly-by command/address/control bus with on-DIMM termination



High precision calibration resistors



Are not backwards compatible-wrongly inserting a DDR3 module into a DDR2 socket can damage the DIMM and/or the motherboard



Advantages compared to DDR2

Higher bandwidth performance, effectively up to 1600 MHz



Higher performance at low power (longer battery life in laptops)



Enhanced low power features



Improved thermal design (cooler)



Disadvantages compared to DDR2



Commonly higher CAS latency

Currently (as of 2008) costs much more than equivalent DDR2 memory