DDR2 - The next Generation of DDR RAM

Taking a quick look back at the recent history of RAM we see that the original SDRAM was a single data rate format. Speeds were the same for the MHz rating as they were for the name of the RAM. For example PC100 ran at a speed of 100MHz and PC133 ran at 133MHz. The single data rate system sent data as the clock cycle rises. DDR (Double Data Rate) was later introduced which as the name suggests doubles the effective data that could be transferred per cycle. This was achieved by sending data on the rising and falling side of the cycle. DDR RAM was quoted as either the effective MHz rating or the memory bandwidth it has. For example DDR-266 memory would be also called PC2100 because the memory module would have a 2.133 Gb/s memory bandwidth. The memory bandwidths were rounded up or down.

DDR2 does not double the data rate again, instead improvements in design and manufacturing have allowed DDR2 RAM to be clocked at much higher levels, up to double again that of the original DDR memory. The following DDR Memory modules are available in DDR2 format.
 

Enhancements on the micro chips themselves allow DDR2 memory to clocked at these much higher speeds. original DDR memory chips would not be physically capable or reaching these types of speeds and would throw up many errors and then simply fail. DDR2 therefore brings memory up to speed inline with current CPU technology, allowing you to keep your system running at an optimal speed.

Due to the nature of the new DDR2 technology these memory sticks are not backwards compatible with the older DDR memory. This means that to use DDR2 memory you will need a motherboard that exclusively supports it. These memory sticks also have different pins, DDR memory has 184 pins while DDR2 has 240 pins. Likewise DDR2 memory slots require DDR2 memory in order to work. make sure you know which memory you require when buying and be aware you may need new memory sticks when upgrading a motherboard.

DDR2 memory comes wit some power saving features that allows it to draw less power than original DDR memory. Active power down mode prevent the memory chips from drawing un needed power. While the total power could be said to be offset by the higher clock speeds, it is apparent that DDR2 memory is certainly more efficient than the older generation of RAM and in most cases draws less actual power as well.

The memory bus width of DDR2 remains the same at 64-bits wide, but most chipsets which utilize DDR2 technology will have dual memory channels, effectively doubling the memory bus to 128-bits wide.

You may be aware that graphics cards have been using DDR2 for quite a while now, However strictly speaking this is not true DDR2 technology, it was developed specifically for graphics cards and does not have all the features that DDR2 has. Graphics card memory is described under the GDDR2 name. GDD3 has been developed recently which has a closer resemblance to the DDR2 memory used for system RAM, it does however have some graphics specific features and again is not the same as