Q: What is the internal structure of the Rainbow?
The Rainbow is an interesting computer in the sense that it is almost two separate computers in one. The Rainbow contains two separate 8-bit buses connected only by 62 Kbytes of shared RAM. Each bus is controlled by one of the Rainbow's 2 CPU's. The Z-80's bus contains the floppy disk drive access and 2Kbytes of dedicated memory. The Z-80 uses the shared RAM to communicate with the 8088's bus.
The 8088's bus connected to many more devices. The video controller is connected to this along with the keyboard controller and port controllers. The video controller has access to 4Kbytes of dedicated RAM. The bus can access both 2Kbyte banks also. When present, the bus has access to the extended memory option board and up to 896KBytes of RAM. The 8088 bus also controls the MFM hard disk controller, graphics option, and Extended Communication Option.