Rainbow PC100+

This describes the technologies associated with the Rainbow PC100+, the machine I am using in WW2014 to read my RX50 collection. Readership is Public

Picture of a Rainbow 100+ in a floor stand The Rainbow 100+ is a personal computer produced by DEC in the early 1980s. My employer in those years procured a lot of them and later on made it possible for staff to acquire them for £100. I got two in September 1988 and used them in various ways for quite a while.

These systems are unusual in that they have two CPUs of different architecture. A Zilog Z80 and and Intel 8088. The firmware also includes VT102 terminal emulation, so they could be used in that way to talk to the VAXen which were my main focus.

The Z80 was used to run CP/M, but I didn't really spend any time with that. Mostly it would boot the 8088 into MS-DOS 2.11. The Z80 still had an active role in accessing the RX50 controller.

The system could be installed in a fibre-glass floor-standing cabinet as illustrated.

The main role of this machine in this Winter Warmup is to read the RX50 disks and stage their contents onto hard disk for cataloging and forwarding on to archive storage.

System components

The entire Rainbow system consists of the system box, a VR241-A Monitor an LK201 keyboard and a special cable to join them up.

This particular system has a 20MB hard disk, "Drive W", for "Winchester" the dual RX50 disk subsystem, 896K of RAM and a graphics subsystem. Picture of Rainbow rear ports.

At the rear are two DB25 serial connectors for communications and printer, the video interface and 7 diagnostic indicators. Observe that there is no network connector.


Picture of VR241-A This unit weighs 16.6kg and the Owner's Guide[1] says that it requires two people to lift it. I have three of these monitors. Its technical specifications as listed in [2] are: Picture of the back of a VR241-A Here's the back of the monitor. It is designed to allow a further monitor to be slaved from it. Incidentally, it is theoretically possible to attach separate text and graphics monitors to a Rainbow, but no external connectors to do that have been provided. Such an arrangement might have been quite useful in those days.


Picture of LK201 I think this is my favourite keyboard. My fingers are used to the spacing, layout and general feel. The shift key is in the right place. Perhaps in a future retrochallenge I'll try to make it usable with all my systems. I have four of these keyboards. There is a lot to say about them and I may expand on this section in the future.


Picture of BCC17 And then there's this thing. It connects the Rainbow's video connector to the VR241-A and the LK201, which plugs into the little socket in the top. I think I used to have gadgets that fixed this assembly to the back of the VR241-A, but they have become hidden somewhere. I have quite a few of these cables - someone once left a box of them on my doorstep.


Picture of PRO-350 badge So that's the Rainbow. This is not the same kind of machine at all as the PRO-350s I have which also would have read the RX50s. But there would be a whole other set of distractions with these - perhaps in another Retrochallenge.


[1] VR241-A Color Video Monitor Installation/Owner's Guide. EK-VR241-IN-001. Digital Equipment Corporation. June 1983.
End user instructions.
[1] Rainbow™ Technical Manual Addendum for models PC100-A, PC100-B and Rainbow 100+. EK-RB100-TM-001. Digital Equipment Corporation. December 1984.
Gives specific technical details about the different Rainbow models.


This document is maintained by Pute. Comments should be addressed to PNJ at XQWV dot ORG dot UK.
  1. PNJ, 2014-01-22. Original version.

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