Hope this answers your question.Q: What is the difference between registered and unregistered SDRAM?
A: SDRAM comes in two varieties - registered and unregistered. The difference is the presence of a clock synchronizing circuit in the registered SDRAM that provides support for the memory system. Memory transfers to and from the processor are transmitted as burst cycles. Four 64-bit transfers between the processor and memory make up a burst. Registered SDRAM synchronizes the system clock and a clock in the memory itself to maintain the proper burst timing. In simple application environments, this feature is less important, therefore offering less expensive unregistered SDRAM enables a more cost-effective solution for the customer. In addition, unregistered SDRAM, though offering less expansion, enables higher performance than registered SDRAM.