Computer History: 1982 DEC Rainbow 100 (A Dual-Processor Personal Computer From Digital)
75Computer History! One of the more rare vintage computers from Digital Corporation (DEC). Lets talk about Digital's personal computer, the DEC Rainbow 100. Released in 1982, it featured 2 processors: Intel 8088 and Zilog Z80. Not entirely IBM PC compatible but enough to run MS DOS (and CP/M 86).
The dual processor design was interesting in that it gave the computer the ability to run two different operating systems: CP/M on the Z80 and MS DOS on the Intel 8088. The machine itself was not fully compatible with an IBM PC and as such MS DOS had to be changed to run. More so, IBM PC applications could not always directly run on the Rainbow without modification, reducing the usefulness of the machine. While it could run CP/M, it came at a time when MS DOS was gaining ground as the definitive operating system due to wide adoption of the IBM PC architecture. That forced even DEC to release IBM PC compatibles later on.
The processors also served other purposes within the machine: The Z80 supports the functions required to read/write the floppy drive. The 8088 handles the video output, keyboard I/O, printer port, and installed optionals.
One design characteristic was the mirrored dual floppy drive system, where the bottom floppy drive was upside down requiring disks to be inserted in that way as well.
For emulating the machine, MAME has some support although it is not perfect.