IBM 1970s and 80s - microcomputers, personal computers. More powerful than the first computers. 1980s and 90s - VLSI chips. Much smaller, much faster. Software Stored program concept - John Von Neumann.
Program resides in the computer rather than on tape, punchcards, etc.
System software - tools to facilitate using the system. Operating system - collection of these tools that manage and abstract system resources. GUIs - graphical interfaces to computers. Sometimes entered via switches. Lights showed the values.