Look up: DDR-SDRAM

1. DDR SDRAM
   Double Data Rate SDRAM can theoretically improve RAM speed to at least 200 MHz. It activates output on both the rising and falling edge of the system clock rather than on just the rising edge, potentially doubling output. This is expected to be the next predominant type of PC memory.
   Found on http://www.mcsx.co.uk/glossary.php
   
   
2. DDR SDRAM
   `Double data rate synchronous dynamic random access memory (DDR SDRAM)` is a class of memory integrated circuits used in computers. DDR SDRAM (sometimes referred to as `DDR1 SDRAM`) has been superseded by DDR2 SDRAM and DDR3 SDRAM, neither of which are either forward or backward compatible with DDR ...
   Found on http://en.wikipedia.org/wiki/DDR_SDRAM
   
   
3. DDR-SDRAM
   Double Data Rate-SDRAM
   Found on http://www.encyclo.co.uk/visitor-contrib
   
   
4. DDR-SDRAM
   Double Data Rate Random Access Memory
   Found on http://foldoc.org/DDR-SDRAM