Linux Fu: Forward To The Past!

Ok, so the title isn’t as catchy as “Back to the Future,” but my guess is a lot of people who are advanced Linux users have — at least — a slight interest in retrocomputing. You’d like an Altair, but not for $10,000. You can build replicas of varying fidelities, of course. You can also just emulate the machine or a similar CP/M machine in software. There are many 8080 or Z80 emulators out there, ranging from SIMH to MAME. Most of these will run on Linux or — at the least — WINE. However, depending on your goals, you should consider RunCPM. Why? It runs on many platforms, including, of course, Linux and other desktop systems. But it also will work with the Arduino, Teensy, ESP32, or STM32 processors. There is also experimental support for SAM4S and Cyclone II FPGAs.

It’s pretty interesting to have one system that will work across PCs and embedded hardware. What’s more is that, at least on Linux, the file system is directly translated (sort of), so you don’t have to use tricks or special software to transfer files to and from CP/M. It is almost like giving Linux the ability to run CP/M software. You still have to have virtual disks, but they are nothing more than directories with normal files in them.


Of course, if your goal is to simulate a system and you want to have 180 kB floppies or whatever, then the direct file system isn’t a benefit. But if you want to use CP/M software for education, nostalgia, or cross-development, this is the way to go, in my opinion.

It isn’t just the file system, either. If you need a quick utility inside your bogus CP/M environment, you can write it in Lua, at least on desktop systems. On the Arduino, you can access digital and analog I/O. Theoretically, you could deploy an embedded Altair for some real purpose fairly cheaply. Continue reading “Linux Fu: Forward To The Past!”

Remembering Ed Roberts, The Home Computer Pioneer You Should Have Heard Of But Probably Haven’t

We’re pretty familiar with such names as Steve Wozniak, Bill Gates, Jack Tramiel, Nolan Bushnell, and the other movers and shakers of the 1970s home computer world. But there’s one person who towered among them for a few years before cashing out and leaving the computer business to pursue the life he’d always wanted. [Gareth Edwards] for Every has a fascinating profile of Ed Roberts, the man who arguably started the home computer boom but is now an obscure figure.

Even if you’ve never heard of Ed Roberts, you’ve likely heard of the product his company brought to market. The MITS Altair 8800 was the first computer to be sold as a home computer rather than for business or scientific use, and though its toggle switch interface now seems extremely quaint, its influence on every microcomputer that followed has been immense.

As followers of the retrocomputing scene, we know about the Altair, but perhaps more interesting is the story of MITS. Formed by a group of US Air Force veterans to produce rocket telemetry equipment, it pivoted to calculators, and as that market imploded in the early 1970s, the computer was a big gamble to save it from bankruptcy. It’s one that paid off, and as someone used to seeing technological cycles of boom and bust, Ed cashed out at the peak of the first wave. He followed his long-held ambition of becoming a doctor, and when, in 2010, he was near the end of his life, the hospital caring for him was shocked to find itself being visited by Bill Gates. It’s an article about a fascinating individual well worth reading.

The Altair, meanwhile, is a project that appears quite often here at Hackaday. Here’s a recreation of one as original as possible. The Mark 8 came out a little earlier but without complete kits or assembled units, so it didn’t get the traction — or the imitators — that the Altair did.

Bootstrapping The Old Fashioned Way

The PDP-11, the Altair 8800, and the IMSAI 8080 were some of the heroes of the computer revolution, and they have something in common — front panel switches, and a lot of them. You probably have a fuzzy idea about those switches, maybe from reading Levy’s Hackers, where the painful process of toggling in programs is briefly described. But how exactly does it work? Well thanks to [Dave Plummer] of Dave’s Garage, now we have a handy tutorial. The exact computer in question is a reproduction of the IMSAI 8080, the computer made famous by a young Matthew Broderick in Wargames. [Dave] managed to score the reproduction and a viewer saved him the time of assembly.

The example program is a Larson Scanner, AKA making an strip of lights push a pulse of light across the strip. [Dave] starts with the Assembly code, a scant 11 lines, and runs it through an assembler available online. That gives us machine code, but there’s no hex keypad for input, so we need those in 8-bit binary bytes. To actually program the machine, you set the address switches to your start-of-program location, and the data switches to your first byte. The “deposit” switch sets that byte, while the “deposit next” switch increments the address and then stores the value. It means you don’t have to key in an address for each instruction, just the data. Get to the end of the program, confirm the address is set to the start, and flick run. Hope you toggled everything in correctly. If so, you’re rewarded with a friendly scanner so reminiscent of 80s TV shows. Stick around after the break to see the demonstration!
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Altair Front Panel Tutorials

If you aren’t old enough to remember when computers had front panels, as [Patrick Jackson] found out after he built a replica Altair 8800, their operation can be a bit inscrutable. After figuring it out he made a pair of videos showing the basics, and then progressing to a program to add two numbers.

Even when the Altair was new, the days of front panels were numbered. Cheap terminals were on their way and MITS soon released a “turnkey” system that didn’t have a front panel. But anyone who had used a minicomputer from the late 1960s or early 1970s really thought you needed a front panel.

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ESP32 Altair Emulator Gets Split Personality

If you wanted me to demo CP/M running on an emulated Altair 8800, I’d pull out a tiny board from my pocket. You might wonder how I wound up with an Altair 8800 that runs CP/M (even WordStar), that fits in your pocket and cost less than $10. Turns out it’s a story that goes back to 1975.

When the Altair 8800 arrived back in 1975, I wanted one. Badly. I’d been reading about computers but had no hands-on experience. But back then, as far as I was concerned, the $400 price tag might as well have been a million bucks. I was working for no real pay in my family’s store, though in all fairness, adjusted into today’s money that was about $2,000.

I’d love to buy one now, but a real Altair costs even more today than it did back then. They also take up a lot of desk space. Sure, there are replicas and I’ve had a few. I even helped work the kinks out of Vince Briel’s clone which I’ve enjoyed. However, the Briel computer has two problems. First, it takes a little work to drive a serial port (it uses a VGA and a PS/2 keyboard). Second, while it’s smaller than a real Altair, it is still pretty large — a byproduct of its beautiful front panel.

So to quickly show off CP/M to someone, you need to haul out a big box and find a VGA monitor and PS/2 keyboard — both of which are becoming vanishing commodities. I made some modifications to get the serial port working, but it is still a lot to cart around. You could go the software route with a simulator like SIMH or Z80pack, but now instead of finding a VGA monitor and a PS/2 keyboard, you need to find a computer where you can install the software. What I really wanted was a simple and portable device that could boot CP/M.

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Altair 8800 Again Project

[Dirk] posted a video (you can see below) titled, “Mystery Retro Project Start.” That turned out to be the first of a multipart series on his Altair 8800 Again simulator. The front panel appears to be laser cut and in some future video episodes, we expect to see him simulate the CPU with a Teensy.

There have been plenty of 8800 clones ranging from projects that recreate the original PCBs, to those that just run a Raspberry Pi inside. The middle ground will use an Arduino or some other small CPU to simulate the 8080 CPU.

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Prolific Videos Show Altair 8800 Recreation

The January 1975 issue of Popular Electronics introduced the Altair 8800 and hit the newsstands in December of 1974, so it is only natural that around the New Year people start thinking about the old computer. [Shadowtron] did more than think about it. He ordered some replica PCBs and is building a new one. Even better, he’s posted an amazing number of videos (up to number 56 as I write this) detailing his progress. You can find part 1, below.

The boards are from Trailing Edge Technology. There’s a backplane board (about $100) as well as a few boards to fit it available for about $30 each — unpopulated, of course.

Continue reading “Prolific Videos Show Altair 8800 Recreation”