Both Bill Gates and Steve Jobs stole from Xerox, specifically from the Alto computer. It was the first graphical operating system — plus it had a mouse.
While it took more than a decade for Microsoft and Apple to develop graphical operating systems, the king of text operating systems in the 1970s was CP/M. It ran on a variety of microcomputers, and was the dominant OS before DOS came on the scene in 1981.
The source code for both operating systems has now been released. You can read the article for more info; the source code is available from the Computer History Museum’s website.
I obtained a copy of the CP/M source code files. They’re written in a language called PL/M, which is high-level so it’s readable. Well, readable by nerds such as myself.
