SDRAM stands for Synchronous Data Random Access Memory. It synchronises to the pc bus speed.

DDR SDRAM is Double Data RAte Synchronous Data Random Access Memory. DDR SDRAM can be accessed by the system on both the upside & downside of a clock cycle. Standard SDRAM can only be accessed on the upside of a clock cycle. The 2 types of RAM are not compatible, your system will use one or the other.

THT