Synchronous dynamic random access memory (SDRAM) is DRAM that is synchronized with the system bus. DRAM has an asynchronous interface, which means that it responds as quickly as possible to changes in control inputs. SDRAM has a synchronous interface, meaning that it waits for a clock signal before responding to control inputs and is therefore synchronized with the computer’s system bus. The clock is used to drive an internal finite state machine that pipelines incoming instructions. This allows the chip to have a more complex pattern of operation than an asynchronous DRAM, enabling higher speeds.

Double data rate (DDR) SDRAM was a later development of SDRAM, used in PC memory beginning in 2000. DDR2 SDRAM was originally seen as a minor enhancement (Based upon the industry standard single-core CPU) on DDR SDRAM that mainly afforded higher clock speeds and somewhat deeper pipelining. However, with the introduction and rapid acceptance of the multi-core CPU in 2006, it is generally expected in the industry that DDR2 will revolutionize the existing physical DDR-SDRAM standard. Further, with the development and anticipated introduction of DDR3 in 2007, it is anticipated DDR3 will rapidly replace the more limited DDR and Newer DDR2.