Operating systems were originally developed using assembly language, which involved direct manipulation of hardware registers. The early UNIX kernel was initially written in PDP-11/20 assembly language but was largely rewritten in the C programming language by 1973, showcasing C's growing power and versatility. UNIX predates DOS, which was considered less advanced due to its lack of features like networking and protected memory that UNIX offered as early as the 1970s. The discussion also highlights that the Xerox Alto was one of the first personal computers to feature a desktop interface and mouse, influencing later systems like the Mac. Overall, the evolution of operating systems transitioned from assembly to higher-level languages, leading to a variety of systems developed in the late 70s and 80s, including Windows, DOS, and Linux.
