Build Your Own Altair 8800 Personal Computer

Go back to 1974 and the dawn of home computing with this Arduino-based kit

5 min read

The Altair 8800 Computer.
Photo: Randi Klett

Altair 8800 ComputerGif: Randi Klett

UPDATE 12 Apr. 2024: Since the following story ran some six years ago, the Altair 8800’s profile has only deepened and broadened. The Canadian Broadcasting Company has written its own tribute to the Altairduino kit, chronicled in detail below, while the semiconductor company MediaTek unveiled their own IoT version of 1975’s ultimate home computer. And lest anyone forget the Altair’s significance, the open-source hardware company Adafruit in 2022 lionized the 8800 as “the computer that birthed MS BASIC and led to Microsoft.” And for those who might actually still own one of these vintage machines, Cybernews estimated in 2021 that it’d probably command at least US $9,000 from a vintage computer enthusiast—probably a bit more than that today, after accounting for post-pandemic inflation.

Other latter-day realizations of the 8800’s significance in computer history have been chronicled across the tech media landscape in the years since Spectrum’s Altairduino article, below. But imitation being the sincerest form of flattery, one might only point to products that recapture the minimalist magic of the hardware—cf. the Compusynth musical synthesizerand the basic (but still pre-BASIC) appeal of its software—cf. the ESP32 Altair emulator—and one can begin to recognize why a still-obscure Bill Gates may have wondered at the flashing red lights back in 1975 and thought to himself, “You know, maybe there’s yet something here.” —IEEE Spectrum

Original story from 23 Feb. 2018 follows:

The MITS Altair 8800 was the first commercially successful personal computer. Created by Ed Roberts in 1974, it was purchased by the thousands via mail order, proving there was a huge demand for computers outside universities and large corporations. Its influence was immense: For example, after seeing the Altair featured on the cover of the January 1975 issue of Popular Electronics, Bill Gates and Paul Allen founded Microsoft (then Micro-Soft) in order to write a Basic interpreter for the new machine.

The Altair sold for US $439 in kit form. Original machines are now collectors’ items that trade for thousands of dollars. Fortunately, there are some cheaper alternatives for people who want to get a direct understanding of the Altair computing experience. Modern kits that replicate the Altair hardware as faithfully as possible are available, as are purely virtual online simulators. Falling somewhere between a replica and a simulation is the $149 Altairduino kit from Chris Davis. The Altairduino duplicates the front panel of the Altair in all its LED- and switch-festooned glory while emulating the internal hardware (including some once fantastically expensive peripherals), using an Arduino Due.

The Altairduino is derived from David Hansel’s work on cloning the Altair with the Arduino Due and Arduino Mega 2560. If you want to build one of Hansel’s designs from scratch, you can do so by following his free instructions on The advantage of Davis’s kit is that it provides all the components, including a nice bamboo case and plastic front panel, along with a custom printed circuit board (PCB) that greatly simplifies construction.



imgLights, Switches, Action: A printed circuit board contains additional circuitry for driving LEDs (top), but most of the work is handed off to an Arduino Due plugged into a rear connector (middle). The finished PCB (bottom) is mounted in the case.Photos: Stephen Cass

The original Altair’s relatively large size means that most of the components are fairly well spaced out on the PCB. Even a beginner could do much of the soldering, although a little bit more experience is required for trickier areas, such as the headers that connect to the Due. The fiddliest bit is adding the LED indicator lights. These are mounted on spacers, and it’s best to put the front panel in place to ensure alignment, which can put you in one of those situations where you really wish you had an extra pair of hands to hold the panel, LED, and PCB tightly together while you solder. The online instructions are detailed and well illustrated, but I would recommend skipping forward and making sure you solder all the resistors in the kit before proceeding to add other, taller, components.

The Altairduino improves on the original Altair in two important respects. First, it offers modern interface options. You can connect an old-school terminal using an optional DB-9 connector (which I will stipulate should properly be called a DE-9 connector, so no need to send me letters this time!), but you can also use a soft terminal running on a computer via a USB connection, or even Bluetooth.

You do the initial configuration of the Altairduino via USB. The instructions are written for Microsoft Windows, so I had to do a little poking around the forums on the Altairduino site to figure out how to get my Mac to talk to the USB interface. Setting the baud rate to 115200 when launching the “screen” terminal command did the trick, and once I set the Bluetooth connection up as the power-on default, it was all smooth sailing.

The second big improvement is that the Altairduino comes loaded with a lot of software. You can call up some programs purely by flipping various front panel switches, such as Kill the Bit, a game that hacked the Altair’s memory-address indicator lights to act as a 1-dimensional display. Other programs are called up with a combination of switch throws and terminal commands. You can quickly fire up Microsoft’s very first 4-kilobyte Basic (which gives you the option, on startup, to disable its sine, random number, and square root functions to save a little memory), or its more advanced 16-KB Basic. The latter has a number of programs you can load from the Altairduino’s memory, including early computer game classics such as Lunar Lander, Star Trek, and Hunt the Wumpus.

You can put additional Altair software on a microSD card, which you plug into a reader that’s soldered to the PCB (Davis conveniently offers a one-stop bundle on his website). Once the kit is assembled, you can’t access the reader to swap out the card without unscrewing the case, but since the universe of Altair 8800 software isn’t growing that rapidly, I’ll manage. (That said, I did just see someone announce they had gotten a Forth compiler running on the Altairduino that I’d like to try.)

The card reader emulates the 88-HDSK hard disk that was available in the business version of the Altair, which sold in the late 1970s for $11,450 to $15,950. A number of disk images are available in the software bundle, including one with the CP/M operating system. The CP/M software also comes with a bunch of software, including parts 1, 2, and 3 of Zork, a pioneering text adventure game.

The Altairduino is a lovely kit that’s an enormous amount of fun—it is surprisingly satisfying to control a computer by flipping switches versus, say, mouse clicks. More seriously, simply looking at pictures of early personal computers, with their blinking rows of lights and bulky cases, can leave the impression they were little more than toys. But engaging with this incarnation quickly demonstrates that the Altair was a capable system, and it becomes much clearer why it was that this machine came to be so critical in establishing the value of personal computing.

This article appears in the March 2018 print issue as “The Altair, Reincarnated.”

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