Double Data Rate Synchronous Dynamic Random Acess Memory
Type of RAM memory derived from SDRAM where two data are transferred per clock cycle instead of only one. Because of this, the performance of this memory is the double of SDRAM performance under the same clock rate.
This kind of memory is found on DDR-DIMM modules.
DDR-SDRAM memories are labeled as DDR200, DDR266, DDR333, DDR400, DDR433, DDR466 and DDR500. The number indicates the memory performance, being the double of the clock rate used. For example, DDR400 memories run at 200 MHz but achieved a performance as if they were running at 400 MHz, hence their name.
It is very important to notice that several times DDR-SDRAM memories are listed as using this “false” clock rate (266 MHz, 333 MHz, 400 MHz, etc).
DDR-DIMM modules use a different kind of nomenclature: PC1600, PC2100, PC2700, PC3200, PC3500, PC3700 and PC4000 (modules using DDR200, DDR266, DDR333, DDR400, DDR433, DDR466 and DDR500 memories, respectively). The number indicates the maximum transfer rate, in MB/s. For example, PC3200 modules have a maximum transfer rate of 3,200 MB/s.
So, while DDRxxx naming system is used to label the DDR-SDRAM memory chip, PCxxxx naming system is used to label the DDR memory module.
