DDR2

DDR2 SDRAM, or Double Data Rate 2 Synchronous Dynamic Random-Access Memory, is a type of memory used in computers and other devices. It was developed by the JEDEC Solid State Technology Association and introduced in 2003 as the successor to DDR SDRAM. DDR2 increases bandwidth by using a four-bit prefetch and higher memory clock rates, while maintaining synchronized operation with a system bus. Compared with DDR, DDR2 operates at lower core voltage—typical 1.8 V, with later low-voltage variants (DDR2L) around 1.35 V for mobile platforms—reducing power consumption.

DDR2 modules support data transfer rates from about 400 MT/s up to 800 MT/s, corresponding to technologies marketed as PC2-3200 through PC2-6400 (various naming schemes reflect different densities and timings). The data path is 64 bits wide on a desktop DIMM, and devices also exist in notebook SODIMM form factors; servers used ECC registered (RDIMM) or, later, load-reduced (LRDIMM) variants.

The architecture features a 4n prefetch, allowing higher data throughput without requiring proportional increases in internal clock speed. This makes DDR2 faster at the same clock rate than DDR SDRAM, though latency can be higher in some configurations.

DDR2 remained common in desktops and laptops through the mid-to-late 2000s, before being phased out in favor of DDR3 and later generations. Today DDR2 is largely obsolete for new systems but may be found in older hardware and retrocomputing contexts.