The Rainbow 100

I grew up with this machine as a child. My father brought one home at some point in the early 1980s to be able to work from home on occasion. He was a pretty big fan of the machines, mostly because he was part of the engineering team at Digital who designed and built the machines. As a little anecdote, he claims full credit for the Rainbow being able to format floppy disks, making it one of only maybe two computers Digital ever built that could format an RX50 5.25" disk...

What's to Love?

These beige boxes don't look particularly notable. In fact, Digital made the wacky decision to make three of their completely incompatible lines of personal computers to look the same (the Rainbow is the only good one of the three, by the way, and I'm not biased or anything...). They are simple to take apart, though, and don't require any tools to get at the motherboard or replace a power supply. They are the exact opposite of the Macintosh or NeXT mindset of "You can't go in there!" However, there's almost no expansion inside, so why would you want to?

Starting a Rainbow is quite an audible joy, though, as it runs the check on its crazy floppy drive. The noises that emanate while the head grinds and switches drives (that's right, one head, two drives!) is easily the most pleasing floppy noise ever.

The machines are famously robust except, perhaps, for the floppy disk doors. They were designed to be left in a barn and still work. Most of mine are still running (I think I own a baker's dozen), but the ROMs are starting to die slowly. The floppy drives do eventually get sticky, but repeated read attempts, believe it or not, seem to get them back to working condition in about 15 minutes in my experience.

What stinks?

Rainbows run MS-DOS and CP/M (and other stuff, but nobody is using anything else, so who cares...). I really don't know why anyone would use CP/M, though. MS-DOS is just better. It has subdirectories!

Anyway, because the machine is a non-IBM-compatible MS-DOS computer, it gets a bad rap. It was never meant to be IBM compatible, so people need to shut it on that front. Getting software running, though, can be frustrating. Also, there is a nearly complete lack of community surrounding these machines. A few people occasionally will ask about them when they get one, but I'm not sure anyone uses or programs on them anymore. So I might be the community...

These computers were business machines, though. It's not suprising nobody is hacking away at the goofy systems.

The graphics hardware on these computers is... unfortunate. They use an NEC 7220, a little, accelerated display processor. Don't listen to those Amiga nuts; the 7220 has hardware-accelerated drawing functions, so they need to shut up about the Amiga having the "first graphics accelerator." The problem, though, is that the graphics memory is not mapped to main memory like IBM PC architectures. To transfer a bitmap to the graphics memory, there's a big delay, which makes graphics "not great" if you want to do things like move sprites. I'm looking into it personally a little bit, but it's unpleasant.

Software and Programming

I do still hack on the Rainbow on occasion. The last thing I really wrote on it and for it was a Breakout clone that ran entirely in graphics mode. It was a fun project and a fun game. I wrote the entire program on a Rainbow using the SeDT text editor, the only text editor on which I ever bothered to learn all the hotkeys. Knowing those hotkeys isn't particularly marketable since they require a Digital keyboard... I compiled the game using Turbo C 2.

I'm typing this nonsense up on one of my beefy Rainbows now. I'm connected via a serial null modem to a Rasberry Pi using BinkleyTerm on the Rainbow. As far as I know, BinkleyTerm is the only Rainbow-compatible terminal software that supports ZModem for transfers, so everyone should be using it.

Other than that, Worm and Ladder on the Rainbow are just the most relaxing games I can play. I also fire up Qix and Solitaire on occasion. I rarely touch Windows on these machines (Version 3.0 works like a dream, a very slow dream, on a stock Rainbow), but it's there, I guess.

I do love these machines. I'll write some more in the future.

> Written on August 4, 2020

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