Playing Doom on a Computer from the 1950s

But can it play Doom? This is one of the first questions technically-inclined individuals ask when they first learn of obscure or ancient computing hardware. It is a sort of litmus test for hackers — if you can get Doom to run on a toothbrush, then you can do anything. And we have seen Doom running on toothbrushes here at Hackster News, and also just about everything else from HDMI cables to seven-segment displays and quantum computers.

Usagi Electric is the king of vintage computers, so it should come as no big surprise that he would eventually want to try to get Doom running on some of his oldest and most obscure machines. After spending many months working to restore a Bendix G-15 to an operational state, Usagi Electric took a break from repairing hardware to work on some software for it. Running Doom on a machine that looks like a refrigerator might not seem as impressive as a toothbrush, but you have to keep in mind that the Bendix G-15 was built in 1956 from vacuum tube and drum memory technology. A modern digital toothbrush is far more powerful.

In fact, the Bendix G-15 is so underpowered for the task, that Usagi Electric had to take some liberty with the phrase “play Doom.” Actually playing the game was out of the question, but it might be able to play the music.

Usagi Electric is much more capable when it comes to hardware than software, so he sought out some help to make this happen. After finding the right programmer, there was the issue of hardware access. Usagi Electric’s Bendix G-15 is likely the only working machine of its type in North America, so how can anyone help remotely? As it turns out, there is an emulator, so that would have to do for a development environment.

A stock G-15 does not actually have any way to output sound, but the original manuals for the machine mention a simple modification that can be made to produce audio outputs. There is also some software in existence that leverages the fact that the drum memory of the machine spins at a constant rate to play data stored in it as musical notes.

The Doom music, however, is much faster-paced, and contains more instruments, than the samples used with this software, like Silent Night. As such, some significant optimizations were needed to make things work. When all was said and done, nearly every bit of the G-15’s memory — 108 words of 18 bits each — was filled with the music playing program and song data.

Finally, the program was punched to a strip of paper tape and loaded onto the machine. After reading it, it played a beautiful rendition of the Doom theme song. So can the Bendix G-15 play Doom? Well, sort of. It is limited to only the music, and at that, none of the original source code — or a translation of it — was used. So it would be more accurate to say that the computer can play a sequence of musical notes, Doom or otherwise. But given the constraints of this early machine, even that is pretty impressive.