DDR 3 Memory
INTRODUCTION
In order to ensure compatibility between memory modules and personal computers, a group called JEDEC (Joint Electron Device Engineering Council) has established standards. With the evolution of computers over their long history, a wide variety of memory standards have been released by the JEDEC group. Most recently they were involved in the establishment of the DDR and DDR2 memory modules. With the DDR2 standard reaching the upper limits of the standard, it was time for a new memory standard to keep pace with processors. This article looks into the newest memory standard, DDR3.
DDR2 vs. DDR3
DDR2 was the successor to the DDR standard. It provided double the speeds of the older memory but at high latencies. It took a while to catch on with the marketplace, specifically because AMD did not really implement it with their Athlon platform until late 2006. Now it is the dominant form of memory used by personal computers. There are limits to the DDR2 standard just as there were with DDR. As a result, the JEDEC established the specifications for the new DDR3 format.
Physically, the DDR3 memory modules will not look all that different from the DDR2 modules. Both will have a total of 240 pins on the memory modules. The only real noticeable difference will be the location of the notch on the module. This is done so that users will not accidently installed the incorrect type of memory into a personal computer.
MEMORY SPEED AND BANDWIDTH
The main purpose for the DDR3 memory standard is to increase the memory speed and bandwidth over the older DDR2 specifications. The original DDR memory modules ran between an effective clock speed of 200 and 400MHz. The DDR2 standards doubled this to between 400 and 800MHz. DDR3 is set to double the speed of DDR2 with clock speeds between 800MHz and 1.6GHz.
Even though the DDR2 memory standard officially only goes up to the 800MHz speed, there are modules that are sold that can run at the 1066MHz speeds. Technically these modules are overclocked standard modules as the JEDEC specs don't officially support speeds over 800MHz. This is often dealt with by requiring the memory modules to run with higher voltages or at different latencies for the increased speeds.
LOWER POWER CONSUMPTION
The other primary benefit of the new memory standard is another reduction in the voltage used to power the memory modules. The original DDR standard modules ran at a 2.5V level. A significant power reduction to 1.8V was created with the DDR2 standard. With the lower voltage levels, personal computers required less actual power to run the memory subsystem. DDR3 looks to further reduce the power usage by dropping the voltage levels to 1.5V. This is not as large of a jump as DDR2 from the DDR standard, but it does reduce the overall power consumption.
INCREASED LATENCIES
In order to increase the speeds of the memory modules with DDR3, it was also necessary to increase the latency of the modules. Latency is the amount of time that it takes for a memory module to process commands in a number of clock or command cycles. The higher the latency, the slower the memory will be at processing a command.
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. Even with the increase in the latency for the DDR3 memory, the higher clock speeds allow the memory to still have a greater bandwidth than the older standards. This results in DDR3 memory running at 800MHz to be slightly slower than DDR2 memory that is also running at 800MHz. The real advantage comes when the clock speeds get higher than this mark.
Another thing with the latencies to be aware of is that these are the standards. As manufacturing improves with the memory modules, the modules will be able to run at lower latencies than the JEDEC specifications. It is possible to find DDR2 memory that is faster than the 5-5-5-15 speeds right now. It will take some time for DDR3 to get below the JEDEC latencies.
Source URL : http://compreviews.about.com/od/memory/a/DDR3.htm
