MS took more than DOS. In the early 80s I had a source code license for the HDOS 2.0 OS used on Heathkit H8 computers. I wrote lots of specialized devices drivers for that OS. The concept of loadable device drivers was stolen directly from HDOS. Likewise, the concept of "mounting" and "unmounting" a disk was stolen. How do I know? The principal programmer for HDOS was JG Letwin. His initials are all over the HDOS source. MS hired JG Letwin to transform the sloppy purchase from People's Computer Company into MS DOS.
I was also a CP/M programmer in that time frame and wrote a few drivers for that OS too. MS did steal a few concepts from CP/M, but not nearly as many as from HDOS.
“I was also a CP/M programmer...”
That’s pretty cool and a good history lesson for me. I think I read that MS copied CP/M API (look and feel) and that is why I thought they stole a lot of the internal code.
Never much of a programmer except for HTML / CSS / Java. More hardware and electronics. But I made some mean batch files in the day. I miss them.