the final major component in the system is the random-access memory, or ram. following its design heritage in sgi supercomputing, the nintendo 64 implemented a unified memory architecture (uma), instead of having separate banks of memory for cpu, audio, and video, as seen on its competitors. the ram itself consists of 4.5 megabytes (0.5 mb for anti-aliasing) of rambus rdram, fabricated by nec. system ram is expandable to a total of 9 mb with the expansion pak. the ram has a 9-bit data bus at 250 mhz; as rdram transfers data at both the rising and falling edge of the signal (a technique also known as ddr), it provides the system with 562.5 mb/s peak bandwidth, shared between cpu and rcp.