1.2.4 RDRAM (N64 Main Memory)

RDRAM is the N64 main memory. It provides a total of 4 megabytes by 9 bits of memory in two chips of 2 megabytes each. You can add another 4 megabytes of RDRAM (another two chips of two megabytes each) by connecting the Memory Pak, which is used by the N64 Game Pak. The CPU and the RCP processing chips share all available RDRAM as shown in the following illustration:

Features of RDRAM

It provides 4 megabytes by 9 bits of space. (The 9th bit is used for anti-aliasing and Z-buffering.)
It consists of several banks in units of 1 megabyte by 9 bits. Each bank has separate active page registers.
The system clock operates at 250 MHz.
It can provide high-speed data transfer of 500 megabytes per second to read or write consecutive data per the RamBUS standard. (Note, however, that this high speed is not attainable for random access.)
The transfer speed is about 200 times that of Super NES.
It can be used simultaneously by the CPU, RSP, RDP, and the RCP I/O interfaces.

RDRAM Block Definition

As a game developer, you can map RDRAM as appropriate for each game application. Usually the following buffers and areas are specified in RDRAM:

Audio buffer
Frame buffer
Z-buffer
Vertex buffer
Texture buffer
Audio command list buffer
Display list buffer
Program area
Other data areas