Rainbow 100

The Rainbow 100 was a microcomputer introduced by Digital Equipment Corporation (DEC) in 1982. This desktop unit had a monitor similar to the VT220 in a dual-CPU box with both 4 MHz Zilog Z80 and 4.81 MHz Intel 8088 CPUs. The Rainbow 100 was a triple-use machine: VT100 mode (industry standard dumb terminal for interacting with DEC's own VAX), 8-bit CP/M mode (using the Z80), and 16-bit CP/M-86 or MS-DOS mode using the 8088.

Models

The Rainbow came in three models, the 100A, 100B and 100+. The "A" model was the first released, followed later by the "B" model. The most noticeable differences between the two models were the firmware and slight hardware changes. The systems were referred to with model numbers PC-100A and PC-100B respectively; later "B" models were also designated PC-100B2.

PC-100A

The "A" model was the first produced by Digital. The distinguishing characteristic of the "A" model from an end-user perspective was that the earlier firmware did not support booting from a hard disk. Other distinguishing hardware features included the three 2764 ROM chips holding the system firmware and the case fan/power supply combinations. Versions of the 100A shipped outside the USA included a user-changeable ROM chip in a special casing. The user changed the built-in ROM for this one to support their keyboard layout and language of the boot screen.