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SDRAM stands for Synchronous Dynamic Random Access Memory and refers to the memory the computer uses to store its data. As opposed to an asynchronous DRAM, the SDRAM is synchronised with the clock speed of the computer in dealing with inputs and is therefore faster. In DRAM, data is stored in separate capacitors and is refreshed at regular intervals. Because of this refresh rate, it is called dynamic.

The advantage of SDRAM is that this type of DRAM tends to increase the number of instructions the processor can execute in a given period of time. The speed of SDRAM is rated in MHz. The read cycle time or the time between successive read operations in an open row determines the speed of the SDRAM. This time has decreased from ten nanoseconds for a 100 MHz SDRAM to five nanoseconds for the DDR-400, but has remained relatively unchanged through the DDR2-800 and the DDR3-1600 generations.

SDRAM also uses another technique in dealing with data known as pipelining. SDRAM chips can accept more than one write command at a time which means that a chip can be processing one command even as it accepts another. The new command has to wait its turn in the pipeline. Earlier RAM chips allowed only one command at a time. In this way, SDRAM chips are faster than their predecessors. This technique has been improved even further by doubling the data transfer rates for every unit of time put forth by the computer’s internal clock, and these SDRAM chips are known as the DDR SDRAMs. In these chips, one transfer takes place at the beginning of the new unit of time while the other takes place at the end. New generations of DDR SDRAMs have improved this rate to four transfers for the DDR2 and eight transfers for the DDR3.

Interestingly enough, though the concept of SDRAM was known as early as the 1970s, it became popular only after Samsung introduced it in 1993. Soon it replaced all the DRAM in personal computers and today the world’s largest manufacturers of SDRAM include Samsung Electronics, Micron Technology, Qimonda (formerly Infineon Technologies) and Hynix.

Most PC systems today use a 184-pin DDR memory. The DR2 SDRAM is the most popular and common type used and though DDR3 motherboards and memory are widely available, they are more expensive than DDR2 products.