CP/M on my TRS-80

> Note: There’s a link to my YouTube video on running CP/M on the Model 100 at the bottom of this article.

One of my favorite pieces of vintage computer technology is the Tandy Model 100 portable computer. I started collecting and repairing these machines a few years ago, and just fell in love with them. They were arguably the first lap-able laptop on the market, amidst an era of luggable computers.

The Tandy Model 100

This machine debuted in 1983 as the Kyocera Kyotronic 85 in Japan. Though it didn’t sell well in Japan, Tandy saw that potential and licensed it to sell it as the TRS-80 Model 100 in the US and Canada. Shortly after, they followed up with an updated version called the Model 102, which was largely the same, but with surface mount components. And after that, they released the Model 200, which was a clamshell form factor that’s more similar to today’s laptops.

My Tandy Model 200, which has a burnt LCD screen that needs to be replaced

The “operating system” for these devices was actually written by Microsoft. It contains a simple menu system with five built-in programs, which include an address book, calendar, text editor, telecommunications program (to work with the built-in 300 baud modem!), and BASIC.

The Microsoft-developed menu system on the Model 100

The machine itself was very popular among traveling business people. Salespeople and journalists in particular were known to use this machine on the road. With a very respectable 20 hours of battery life on 4 AA batteries, it really was a great portable computer that could be used for remote work.

Model 100 Ad in the Summer 1983 Radio Shack Catalog

Despite the small 8-line, 40-character display, it’s a great machine. Even in modern times, it serves as a fine foundation for basic text editing or writing tasks. In fact, there are many people that use the Model 100 today as their main writing tool. There’s an active community of M100 enthusiasts who have created chips and other add-ons that give the Model 100 additional capabilities. For example, the TPDD Backpack allows you to save files to an SD Card, while the REX# enables you to emulate ROM chips to run third party software.

The REX# (left) and TPDD Backpack (right)

One project in particular that I came across a couple of years ago really caught my eye. One of the guys in the Model 100 community created a chip that enables the device to run the CP/M operating system. If you’re not familiar with CP/M, it’s an early DOS-like operating system from the 1970s. If you’ve used MS-DOS, then CP/M is going to be familiar to you. Microsoft purchased a different operating system in 1981 called 86-DOS, and rebranded it as MS-DOS. The creator of 86-DOS used CP/M as an inspiration for how he designed it to work. So as a result, MS-DOS inherited a lot of the same characteristics of CP/M.

I was very intrigued, so I reached out to the creator of this chip, Stephen Adolph, and purchased one. I spent some time with it and I have to say that it’s one of the coolest mods I’ve seen for this device. To share my experience with you, I created a YouTube video that takes you through the process l used for installing the chip, loading it up, and running CP/M. I hope you enjoy watching this video as much as I enjoyed making it!

Check out my YouTube video on running CP/M on the M100!

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