off entirely. Variants Double data rate memory Double data rate (DDR) memory controllers are used to drive DDR SDRAM, where data is transferred on both rising and falling edges of the system's memory clock. DDR memory controllers are significantly more complicated when compared to single data rate controllers , but they allow for twice the data to be transferred without increasing the memory cell's clock rate or bus width. Multichannel memory Multichannel memory memory controllers are memory controllers where the DRAM devices are separated on to multiple different buses to allow the memory controller(s) to access them in parallel. This increases the theoretical amount of bandwidth of the bus by a factor of the number of channels. While a channel for every DRAM cell would be the ideal solution, adding more channels is very difficult due to wire count, line capacitance, and the need for parallel access lines to have identical lengths. Fully buffered memory Fully buffered memory systems place a memory buffer device on every memory module (called an FB-DIMM when Fully Buffered RAM is used), which unlike traditional memory controller devices, use a serial data link to the memory controller instead of the parallel link used in previous RAM designs. This decreases the number of the wires necessary to place the memory devices on a motherboard (allowing for a smaller number of layers to be used, meaning more memory devices can be placed on a single board), at the expense of increasing latency (the time necessary to access a memory location). This increase is due to the time required to convert the parallel information read from the DRAM cell to the serial format used by the FB-DIMM controller, and back to a parallel form in the memory controller on the motherboard. In theory, the FB-DIMM's memory buffer device could be built to access any DRAM cells, allowing for memory cell agnostic memory controller design, but this has not been demonstrated, as the technology is in its infancy. Flash memory controller Many flash memory devices, such as USB flash drives and solid state drives, include a flash memory controller. Flash memory is inherently slower to access than RAM and often becomes unusable after a few million write cycles, which generally makes it unsuitable for RAM applications. See also Memory scrubbing MMU Address generation unit Multi-channel memory architecture References External links Infineon/Kingston (a memory vendor) Dual Channel DDR Memory Whitepaper