rambus technology was quite new at the time and offered nintendo a way to provide a large amount of bandwidth at a relatively low cost. the narrow bus makes board design easier and cheaper than the higher width data buses required for high bandwidth out of slower-clocked ram types (such as vram or edo dram); this way, the n64 mainboard could be designed with only 2 layers. however, rdram, at the time, came with a very high access latency. the combination of high bandwidth and high latency meant that significant effort was required from developers to achieve optimal results. early n64 revisions use two 18 mbit ram chips; in ca. 1998 these were replaced with a single 36 mbit chip, same as was used on the expansion pak.