Time sharing enables large computers to interact with and perform tasks for many users at such a fast rate that users are practically unaware the computer's time is divided. Before the development of time-sharing systems in the 1960s, computers were generally large and expensive and ran only one program at a time. Users took turns on the computer. Running a single program could take hours because it involved manually setting up the whole computer system: computer, tape drives, card punchers and readers, and printers. An iterative computer task, such as debugging a program, could take many lengthy sessions with the computer. During setup, the computer itself sat idle--a waste of an expensive, valuable resource.

Operating systems (OS) and batch processing were early developments that made computers more efficient. Operating systems were developed in the mid-1950s as sets of special computer programs that controlled...