DDR vs. DDR-2

This is one of the biggest points that separate both AMD and Intel. While we will be talking about both systems here, we won’t actually be testing the AMD, simply because it doesn’t support DDR-2 and is not likely to for some time.

DDR-2 is the evolution of the DDR memory standards. First off let’s take a brief look over the two technologies and their main differences. In order to increase the overall data transmission throughput without having to increase the speed of the memory is to actually increase the internal data rate of the cell array. DDR-2 uses two cells running in parallel; each cell uses two bits, making it a 4 bit total cell whereas DDR only has a 2 bit process. In order for the data buffer to keep up, the buffers run at twice the cell array speed. This overall process allows for DDR-2 to run at an effective clock rate 4x that of the actual memory modules. What this means is DDR-2 memory with a 400MHz rating is actually running with cells running at a clock speed of 100MHz which would be 200MHz with regular DDR.

The next major addition to DDR-2 is On-Die signal termination. One of the biggest problems with DDR1 was compatibility with other modules in most cases and in a few others with motherboards. This was because of the Signal termination. DDR memory used a series of resistors on the motherboard in order to terminate the bus signal noise on the memory channel. The problem with this is two fold:

1) When using modules from different manufacturers, if one module sent too much noise through the bus line to the additional memory module you could get memory instabilities.

2) If the motherboard didn’t use enough of the right resistors or use ones of inferior quality, the board would cause memory stability problems.

DDR-2 actually puts the termination for the bus signals on the modules themselves. This means that modules can be mixed and matched between manufacturers with relative ease. Another great feature is that the signal termination is closer to the memory modules, allowing for less noise on the bus and allowing for faster speeds due to a cleaner signal.