The DEC Rainbow 100 is packed with option boards. I've taken pictures of the mainboard, the floppy controller, the HD controller (MFM), the graphics board and the memory expansion.
The keyboard is (again) non-standard, F3 enters a monitor, Ctrl-F3 is the warm start. Pictures DEC Rainbow 100
The small 4K ROM actually has a DEC marking on it ... 23U37E300 ... missed it the first time, sorry.
I've re-dumped the ROMs that Micko mentioned in one of his last posts, but will re-do them again soon. More ROM dumps of the DEC Rainbow