Two kinds of system memory are shipped in today's PCs and portable computing devices: DDR3, and its older sibling, DDR2. Although both have advantages, DDR3 is the winner if judged strictly on technology. DDR3 can provide up to twice the bandwidth than DDR2, requires less power (1.5 volts versus 1.8 volts), and has more headroom for future increases in speed.
DDR3 also touts more subtle advances, such as a reset pin in the event that a module locks up. It also doubles the prefetch buffer and offers a feature called ZQ calibration, which tunes the memory to the system temperature and voltage to ensure top performance and reliability. And if speed is your sole criterion, DDR3 is still the winner.
However, don’t count out the venerable DDR2 standard just yet, though. It’s cheaper to implement than DDR3. And even though DDR2 memory is only slightly less expensive per gigabyte than DDR3, associated technologies—such as CPUs and chipsets that support DDR2— have been on the market a long time and are cheaper than their DDR3 equivalents. This makes DDR2 products cheaper to produce (and therefore, cheaper to buy) than DDR3 products, at least for now.
And DDR2 is still quite fast, easily zippy enough to perform most jobs. Even benchmarked, the performance differences in real-world scenarios between DDR2 and DDR3 have proven slight. The discrepancy in speed is typically not something you’ll be able to spot with the naked eye.
DDR3, however, has a few other tricks up its sleeve. For instance, it draws less voltage than DDR2, which can extend battery life in laptops and netbooks—reason enough to make DDR3 an appealing choice for portable products. If that’s not enough, consider this: DDR3 chipsets and the like tend to have more advanced features and better performance than older DDR2 models, meaning that DDR3 netbooks and notebooks will generally be faster—or at the very least, packed with more goodies—than a system featuring DDR2.
DDR3 is making its way into midrange and lower-end products as Intel's Core series CPUs (which require DDR3) are becoming more common. But there are still plenty of DDR2 devices available, and there's an obvious financial incentive for choosing them.
Simply put, DDR3 is the technology of the future. At some point, it will supplant DDR2 entirely. In the meantime, though, DDR2 remains viable if you want to upgrade or need to replace your memory.