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RAINBOW 100

The Rainbow 100 had a proprietary floppy drive format. Disks formatted for the Rainbow 100 could not be read or written to by other PC computers, even though materially they were the same type of 5'' disk.

Chris Ryan reports:

There were two versions : the model 100 and the model 100+. The 100 had 64 KB soldered RAM and the 100+ had 128KB with a socket expansion for an other option board.

The system was triple boot (in BIOS, and could be set for automatic default boot preference on 100+) and booted in either CP/M, DOS, or VT100 mode.
When booted in DOS, the Z-80 acted as an I/O co-processor for the 8088 side, and visa-versa for CP/M mode.
The 8088 could also be upgraded with an NEC V-20 chip, but it involved either doing an E-PROM hack (published) or manually selecting the boot mode each time. (It was due to the V-20 being so much faster, and the post used a step/increment timing sequence, the system would respond faster than the number of clock cycles it was told to wait until looking for a response.)