With the introduction of DDR2 RAM, there are always questions hovering in the mind "Should I upgrade my memory to DDR2? Is it better?" Hopefully this article will shed some light to your queries and help you make a better decision.

The difference between DDR and DDR2

Both DDR and DDR2 RAM are the improved version of the SDRAM. They are able to transmit data on the rising and falling edge of the clock cycle. The conventional SDRAM can only transmit data on the rising edge. For a certain clock frequency, say 100MHz, both DDR and DDR2 RAM can operate at double the clock frequency, i.e. 200MHz. The difference of DDR2 to DDR is a doubled bus frequency for the same physical clock rate, thus doubling the effective data rate another time. This means that for a 100MHz clock frequency, a DDR2 RAM can achieve a speed of 400MHz while DDR RAM only achieves 200MHz.

Is DDR2 much faster?

Theoretically, DDR2 RAM should perform better than DDR since it clocks a higher speed. The actual fact is: this may not be true. There is this term known as ‘latency‘ that is affecting the performance of the RAM. Latency refers to the amount of time needed to fetch the data. All RAM running at the same clock frequency will have the same latency, only the bandwidth differs. This means that a DDR2 400MHz module has the same latency as a DDR 200MHz RAM.

This is where the interesting part comes in. A DDR 400MHz has a clock frequency of 200MHz. When compare to a DDR2 400MHz with a clock frequency of 100MHz, the DDR 400MHz module apparently has a lower latency than the DDR2 400MHz RAM. This means that the DDR 400MHz module actually performs much better than the DDR2 400MHz module as concerns the time of accessibility of the data.

DDR2 is potentially faster, since it provides a much higher bandwidth. But their latency also goes up as the speed increases. In fact, its true benefit only shows in higher frequency modules such as DDR2 667MHz and DDR2 800Mhz. Comparatively, a DDR 400Mhz RAM still performs better than a DDR2 400Mhz or DDR2 533MHz RAM.

Heat Dissipation

All is not lost yet. DDR2 has a feature that is worth mentioning. It works at 1.8V, compared to 2.5V for DDR RAM. This means a 30% reduction in the heat consumption. Well, if you are using 64MB or 128MB of RAM, this doesn?t add up to anything. But if you are installing 1GB, 2GB or even 4GB of memory to your system, the heat consumption will escalate to a whopping number. This is definitely worth considering.

Below is a small chart which outlines the major differences of the two types of memory.

	DDR	DDR2
Data Bus	64 bits	64 bits
Data Rate	200/266/333/400 Mbps	400/533/667/800 Mbps
Bus Frequency	100/133/166/200 MHz	200/266/333/400 MHz
DRAM Frequency	100/133/166/200 MHz	100/133/166/200 MHz
Densities	256MB 512MB 1GB	256MB 512MB 1GB
Voltage	2.5V	1.8V
Prefetch Size	2 bits	4 bits
Burst Length	2/4/8	4/8
CAS Latency	1.5, 2, 2.5	3+, 4, 5
Write Latency	1T	Read Latency -1

From this chart, you can see that DDR2 begins at 400MHz up to current 800MHz while DDR stops at 400MHz. As a result, its latencies were doubled in order to make place for the higher bandwidth.

Conclusion

Without doubt, DDR2 will be the standard for future RAM. More and more motherboards are starting to shift to DDR2 technology and it?ll be a matter of time before DDR is phased out. It?s advisable to get DDR2 667 or 800 RAM as they have a better performance than DDR, making it more worthwhile for the upgrade.