Specifications

CHAPTER 2
Architecture
20 Block Diagram and Main ICs
Display RAM 2
The display memory in the Macintosh Performa 6400 computer is separate from the
main memory. To reduce the cost of the computer, the display memory is implemented
with DRAM devices instead of more expensive VRAM devices. The display memory
consists of 1 MB of 60 nanosecond (ns) DRAM devices configured to make a 32-bit data
bus. The display memory cannot be expanded.
The display memory contains three separate frame buffers. The first frame buffer holds
the graphics data—the display that is generated by the computer. The other two frame
buffers hold video data from the video input module. The video data frame buffers are
used alternately: while one is supplying data to be sent to the video monitor, the other is
receiving the next frame of video input.
The display data generated by the computer can have pixel depths of 4, 8, or 16 bits for
monitors up to 800-by-600 pixels and 4 or 8 bits for larger monitors up to 1024-by-768
pixels. Data from the video input module is always stored and transferred at 16 bits per
pixel. The video frame buffers support live video in a 320-by-240 pixel frame at 30
frames per second.
Note
The Macintosh Performa 6400 computer cannot display live video from
the video-in module on monitor sizes larger than 800-by-600 pixels.
Apple Computer, Inc., does not recommend the use of such monitors for
these applications. ◆
The Macintosh Performa 6400 computer can display video in a window inside the
computer graphics display. The Valkyrie-AR IC has registers that contain the starting
location of the video window within the display, the starting address of the video data in
the video buffer, and the size of the video window.