I actually wrote two operating systems in assembler: one was for a Nova 1200 for final project in operating systems, and the other was a graphical operating system for a CDC 1700 with attached CDC 774 graphics terminal written for my masters thesis.
In both cases the only tool was a cross-assembler, both of which ran on a CDC 6400. The output for the Nova 1200 was punched to paper tape which was then read in from a paper tape reader on the Nova 1200 by hand togging in it’s driver each time. For the CDC 1700/774, there was a computer-to-computer hardware link between the 6400 and the CDC 1700 and the link’s driver had to be hand togged in each time. There were errors and omissions in the link’s documentation and I had to get the onsite CDC engineers to look at its circuit diagram to figure out how to make the damn thing work.
The Nova 1200 OS was written in one college quarter, and the CDC 1700 was written in a few months. That was back in the day when programmers were real men.
Hey, I STILL use Assembly Language for programming. Love it. Now I am trying to convert some of the old programs I wrote in Basic back in the TI-99/4A days to run under linux using Visual C++ and it’s a chore.
The fact that these people wrote a light and fast OS in assembler that can actually work stably with all the hardware out there today, using a GUI no less, and will run Quake and Doom as well is truly impressive.
Yeah, when we ran out of zeros, we used capital O’s. :=)