30 July, 2009

RAM Choices - DDR2 or DDR3 ?

The memory market is in the process of transitioning from DDR2 memory to the more efficient and higher density DDR3 technology; this process will be underway until the end of the year. DDR2 is available at 800 and 1066 speeds, while DDR3 reaches from 800 to 1333. Faster products are still enthusiast-class premium products, as no platform offers official support for 1600+ speeds yet.

Both technologies are based on the double data rate principle, which means that they transfer data twice per clock cycle: during the rising and falling edge of the clock signal. Each new DDR memory generation is based on smaller transistors, decreased voltage levels and higher memory density. While the internal clock speeds don’t change, the clock speed at the interface (I/O buffer) has been increasing due to an increasing level of what is called prefetch. DDR3-1600 memory works on a physical memory clock of 200 MHz, but at a prefetch of eight. The interface runs at 800 MHz, but thanks to double data rate mode, this equals a 1600 MHz frequency. DDR2-800 also runs at a 200 MHz base clock, but with a prefetch of four.
As already mentioned, performance shouldn’t be the primary reason to switch from one memory generation to the next. Memory densities, however, are more interesting. While 1 GB DIMMs (1 Gbit ICs) can be considered mainstream in the DDR2 market, DDR3 memory will be the dominant technology once 2 GB DDR3 DIMMs become affordable, and once AMD has switched to it as well, later this year.

Which Memory Should You Buy?
However, the best deals on memory can clearly be found in the DDR2 mainstream. If budget is an issue, any 2x 1 GB DDR2 brand memory kit at DDR2-800 speed will do the job perfectly well. As you will see in the benchmark section, only significantly faster (and significantly more expensive) memory can deliver a tiny performance advantage. We don’t even recommend going for DDR3 motherboards, unless you’re purchasing something in the high-end. When you’re looking at several hundred dollars for a motherboard, and similar price points for a Core 2 Quad processor and decent system components, it is acceptable to spend some more on the memory. For anyone with a limited budget, though, it’s not.
2 GB memory kits offering two DDR2-800 modules start at approximately $75, which can be considered a bargain given that 2 GB of main memory is enough to run all sorts of mainstream applications and games. More memory, meaning 4 GB, requires a 64-bit operating system, because Windows XP and Windows Vista will only be able to handle 3 GB RAM when the 32-bit versions are used. Although the 64-bit versions are equally reliable, almost equally fast, and driver support has improved a lot, be sure you double check if your devices and applications will work in a 64-bit environment.