Bare Metal Programming

I used to get a kick out of the recollections of the slightly older guy I worked with (Rob Weinberg). He used to tell me about programming on a system where they didn’t even have a keyboard. As he explained it, the computer was programmed by flipping switches for each bit and pushing a button to store assembly instructions. This would be done repetitively until all the instructions were entered into the computer and then the “program” could be run. I thought that was really funny having started with 4GL programming. Well I ran across a couple of videos on youtube of a guy programming a Dec PDP computer which was the machine that was in use just before I started my career on Dec Vaxen. And the videos show how it was done. (you younger guys might want to sit down before you watch this, I don’t want anyone to get dizzy and hurt themselves)

The switches allowed assembly language to be input (looks like 4 – 3 bit characters to me). They also had the ability to read programs off of paper tapes as long as you could enter the program to read the tape. Here’s a guy doing just that.

If you want to see what a variac is, have a look at this one:

It’s basically a power conditioner. I’m not sure why they needed that. I have seen people use them with guitar amps which can be sensitive (from a sound perspective) to low voltage or variable voltage.

Anyway, I thought the videos were entertaining.


  1. joel garry says:

    My first computer had dual 8″ floppies. A bit smaller than this one, but similar model:

  2. Michael Fontana says:

    I don’t think I can top Rob’s story since he had real-world experience, however, in 1977, while attending college at the State University of New York in Albany, we had to create our own assembly language doing much the same thing on a then-ancient Univac-6 computer built about 20 years previously. We then had to write a computer program using this language, and could choose from several projects. Mine was a celsius-to-farenheit temperature conversion. I think it took over 1000 punched cards to get the job done.

    Our instructor was certain this experience would help us in the business world, but it never really did. By the time I started working, punch-cards were nearly gone. I think I used them for about four weeks, but I met a lot of then old-timers who refused to use CRT terminals or workstations.

  3. Dominic Delmolino says:

    My high-school had that exact same model — during my school years I used to help out with the school’s “IT” department and one of my first lessons was how to start up that machine 🙂

Leave a Reply to Dominic Delmolino