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. The CPU and the RCP processing chips share all available RDRAM as shown in the following illustration:

Figure 2-4-1 The N64 hardware block(RDRAM)

2-4-1 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.
• The transfer speed is about 200 times that of Super NES.
• This high speed is not attainable for random access.
• It can be used simultaneously by the CPU, RSP, RDP, and the RCP I/O interfaces.

2-4-2 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

Figure 2-4-2 RDRAM Block Definition