[animatedb]

I imagine you may know a lot about this, but what OS/machine were they using to develop it? PDP-11?, CPM? What editors did they use? Line editors? Which machines did they use to test on? Most drives and even RAM was unreliable back then and everything was small. I imagine there were plenty of obstacles back then. I remember using CPM where floppy disks had to be swapped between the editor and compiler, and your program may fit on another floppy disk.

[WalterBright]

There are clues they may have used Unix at some point, but the books I've read were vague about that. As the blog post points out, apparently they used MASM that ran on DOS, meaning they were using the IBM PC as the development machine.