PC Stats has posted an introduction to DDR-2: The DDR Memory
Replacement

DDR2-SDRAM is considered an evolutionary upgrade over existing DDR memory. It maintains the same core functions, transferring 64 bits of data twice every clock cycle for an effective transfer rate twice that of the front-side bus (FSB) of a computer system, and an effective bandwidth equal to its speed x 8. Of corse, DDR2 introduces some new features which allow it to ramp up to much higher speeds (with correspondingly higher bandwidth) and higher memory densities, all the while using less power. Sounds good doesn't it? Let's look at the 'big' facts first, before we explore the memory in detail. DDR2 memory uses a new form factor, a 240 pin DIMM (Dual Inline Memory Module) which is *not* compatible with current DDR memory slots. Upcoming chipsets by Intel and other manufacturers will support DDR2 specifically, and are not backwards compatible.

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