SDRAM stands for Synchronous Dynamic Random Access Memory, and it is a fast method of delivering computing capacity. It can run at 133 Mhz, which is much faster than earlier RAM technologies.
This type of memory is very protective of its data bits, storing them each in a separate capacitor. The benefit of this is that it avoids corruption and maintains "pristine" data. The drawback is that those same capacitors that are so useful at storing the SDRAM bits also happen to be very bad at keeping electrons in check; the result is where the Dynamic part of the name comes in, as refreshes are required to maintain data integrity. Once all of that dynamic refreshing and storing is done with, the result is a dense package of data, one of the densest in the business world.
The Synchronous part of the name is added with a subroutine that lines itself up with the computer system bus and processor, so that all operations take place at the same time. Specifically, the computer's internal clock drives the entire mechanism. Once the clock sends out a signal saying that another unit of time has passed, the memory chips go to work. In addition to the dense data package of DRAM, it allows a more complex memory pattern, resulting in an extremely powerful method of storing and accessing data.
Another benefit of SDRAM is what is called pipelining. Because the chips are so dense and complex, they can accept more than one write command at a time. This means that a chip can be processing one command while it accepts another one, even if that new command has to wait its turn in the pipeline. Previous RAM chips required proprietary access, allowing only one command at a time throughout the chip. In this way, the chips are faster than their predecessors.
This mostly describes single-data chips, or SDR SDRAM. An even newer kind of chip is double-data-rate, or DDR SDRAM. This allows for even greater bandwidth by making pipeline data transfers twice for every unit of time put forth by the computer's internal clock. One transfer takes place at the beginning of the new unit of time, and the other takes place at the end.
SDRAM chips first came to the computing forefront in 1997. In just three years, they had become the dominant force in memory chips across the computing spectrum.