The Rainbow 100 was a microcomputer introduced by Digital Equipment Corporation in 1982 to compete in the IBM PC market. This desktop unit had the video-terminal display circuitry from the VT220 in a box with both Z80 and 8088 CPUs. The Rainbow 100 was a triple-boot machine: VT220 mode, CP/M mode (using the Z80), and CP/M-86 or MS-DOS mode using the 8088.

A typical entry-level configuration was with 128Kb memory and two floppy disk drives.

The Rainbow 100 and the other two microcomputers which it announced at the same time (DECmate II and Pro-350) had two quirks that annoyed conservative users. The LK201 keyboard used a new layout that made some ASR33 and VT100 users unhappy. However, the VT220 style of this keyboard can clearly be seen in the layout of the enhanced 101-key keyboard adopted by IBM in 1987. The floppy disk drives took 400K single-sided quad-density disks when all the other microcomputers were using 360K double-sided double-density disks. Initially users had to buy media from DEC with a special reinforcing ring at the hub, but this became unnecessary when other manufacturers starting producing diskettes that suited both types of drive.

A benefit of the Rainbow was that it could continue to run 8-bit CP/M software as users moved into the 16-bit world of MS-DOS. The disadvantage was that little DOS software was released on Rainbow media and there were subtle differences between MS-DOS, as run on a Rainbow, and MS-DOS (or PC-DOS) running on true IBM PC compatibles. Towards the end of its life, Rainbow users were able to run IBM PC compatible MS-DOS software using an emulation application, which obviously defeated the purpose of having the twin-CPU design.

External links

• Vintage-Computer page on the DEC Rainbow 100

Personal computers | DEC hardware