After recently reviewing the Gigabyte 8GPNXP motherboard, I received a whole heap of e-mails regarding the boards dual memory support. It would seem that a lot of people are unsure about the differences between the original DDR memory and the new DDR2 memory type. Most of the questions were Which memory type is faster?, Can both DDR and DDR2 be used at the same time? and of course Which memory should I buy?. In todays article I hope to clarify all these questions and shed some more light on the situation. Most will be surprised to find that there is not a great deal of difference between DDR and DDR2. First here is some history regarding the original DDR memory standard.

The name DDR stands for Double Data Rate. DDR memory works by carrying information on the rising and falling point of a clock cycle, where as the much older SD-RAM carried data at only the rising point of each cycle. Theoretically, this means that DDR memory has double the memory bandwidth. The first DDR memory was rated PC1600 which ran on a 100MHz memory clock, this enabled it to produce a maximum data bandwidth of 1600MB/s. The next step was PC2100 which ran at 133MHz which resulted in a maximum transfer of 2100MB/s, and then PC2700 which operated at 333MHz giving a peak bandwidth of 2700MB/s. Many more standards emerged, while the official standard for DDR memory ended at PC3200 (DDR400), memory manufacturers went well beyond this. There were a number of memory manufacturers that offered memory as fast as PC4400 (DDR550). This kind of memory was strictly aimed at overclockers.

The new DDR2 memory picks up where the original DDR memory left off, starting at DDR2 400 it is already available at 677MHz. While DDR2 is almost identical to DDR memory there are a number of enhancements. The biggest feature of DDR2 is its 4-bit prefetch, allowing it to read/write four times the amount of data per clock cycle. This feature effectively doubled the data bus speed while keeping the same 64-bit interface that the original DDR memory used.

This new DDR2 memory has been available for quite some time now, but it will not overtake its predecessor for quite some time. The demand for DDR2 has really only grown over the past few weeks and suppliers are now having problems with DDR2s availability. DDR2 memory cannot simply replace original DDR memory modules due to the physical difference in the pin count, as DDR has 184- pins and DDR2 has 240-pins. The power requirements are also different, as DDR2 requires less power to operate at higher frequencies.

Now I believe the biggest cause for confusion regarding this new memory type, are the CAS Latencys. Although DDR2 features a 4-bit prefetch, we are still finding it unable to out perform the original DDR memory at the same or similar frequencies. For example DDR400 is capable of operating with timings of CAS2-2-2-5 where as standard DDR2 400 at the moment runs at CAS4-4-4-12. This means that despite the fact DDR2 maybe working harder delivering twice as much data per clock, it is theoretically doing it twice as slow due to the poor latency timings.

This means it will not be until DDR2 667 becomes a standard that we will truly see DDR2 take charge. At this frequency it is believed that poor latency timings of DDR2 will no longer plague it, as the frequency will aid its performance. However this does leave me with the same questions I have been asked time and time again. What should you do now? DDR and DDR2 memory modules can not be used simultaneously. Therefore it makes little sense to replace current DDR 400 memory modules with DDR2 533 modules. Nevertheless I have included a number of benchmarks to explore the physical performance differences between these two memory types.