The Rainbow 100 was a microcomputer introduced by Digital Equipment Corporation (DEC) 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. Digital Equipment Corporation was a pioneering company in the American computer industry. ... The VT220 was a terminal produced by Digital Equipment Corporation from 1983 to 1987. ... One of the first Z80 microprocessors manufactured; the date stamp says well before July 1976. ... An Intel 8088 microprocessor The Intel 8088 is an Intel microprocessor based on the 8086, with 16-bit registers and an 8-bit external data bus. ... CP/M is an operating system originally created for Intel 8080/85 and Zilog Z80 based microcomputers by Gary Kildall of Digital Research, Inc. ... CP/M-86 was a version of the CP/M operating system for the Intel 8086. ... Microsofts disk operating system, MS-DOS, was Microsofts implementation of DOS, which was the first popular operating system for the IBM PC, and until recently, was widely used on the PC compatible platform. ...

The Rainbow came in three models, the 100A, 100B and 100+. The 'A' model didn't allow for a hard disk controller, whereas the 'B' allowed this option and the '+' shipped with the controller and a hard drive.

A typical entry-level configuration was with 128 KB memory and two floppy disk drives. A kilobyte (derived from the SI prefix kilo-, meaning 1000) is a unit of information or computer storage equal to either 1024 or 1000 bytes. ...

The Rainbow 100 and the other two microcomputers which DEC 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 400 KB single-sided quad-density disks when all the other microcomputers were using 360 KB 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. Of note was the single motor used to drive both disk drives, which were arranged one on top of the other. A PDP-8 compatible microcomputer introduced in 1982 by Digital Equipment Corporation. ... A PDP-11 compatible microcomputer introduced in 1982 by Digital Equipment Corporation. ... The new style keyboard, introduced in 1982, used by Digital Equipment Corporations VT220 ANSI/ASCII terminal. ... Introduced about 1963, Teletype Corporations ASR33 was a very popular model of teleprinter. ... The VT100 was a video terminal made by Digital Equipment Corporation (DEC) which became the de facto standard used by terminal emulators. ... The enhanced keyboard was first made by IBM; it has over 101 keys and is now the standard keyboard for PCs. ... A 3,5 inch diskette, removed from its casing A floppy disk is a data storage device that is composed of a disk of thin, flexible (floppy) magnetic storage medium encased in a square or rectangular plastic shell. ...

Various Rainbow option upgrades were available from DEC including a high resolution colour graphics card (driving an RGB DEC monitor), ST-506 hard drive controller and drive (typically 5, 10 or 20 MB), a memory expansion module expanding memory up to a maximum 896 KB, a 8087 math co-processor upgrade and a DECNet network adapter. The ST-506 was the first hard disk intended for use specifically on microcomputers, introduced in 1980 by Seagate Technology. ... A megabyte is a unit of information or computer storage equal to approximately one million bytes. ...

Third party upgrades were also available including a 80286 processor upgrade and 3.5 inch disk adapter kit.

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 called Code Blue. Microsofts disk operating system, MS-DOS, was Microsofts implementation of DOS, which was the first popular operating system for the IBM PC, and until recently, was widely used on the PC compatible platform. ... IBM PC-DOS was one of the three major operating systems that dominated the personal computer market from about 1985 to 1995. ... One of the first PCs from IBM - the IBM PC model 5150. ...

Of note is that Windows version 1.0 was ported to the Rainbow by DEC. There was also a 3rd party upgrade that included a 286 processor board and a modified version of Windows 3.0.

External links

• Vintage-Computer page on the DEC Rainbow 100