By the early 1960s, technology had progressed to the point, where computers could work on several programs at a time, and time-shared operating systems emerged as a viable platform for programming and running applications. Several terminals (keyboard/printers) were connected to a single computer running a time-sharing operating system. Programmers entering instructions or data entry operators used the terminals. They received immediate feedback from the computer, increasing their productivity.
Let’s say there were ten programmers working at their own terminals. The operating system would spend a small “slice” of time – say a twentieth of a second – on one job, then move to the next one. If a programmer was thinking or doing something else when his or her time slice came up, the operating system skipped them. Since the time slices were short, each programmer had the illusion that the computer was working only on their job and they got immediate feedback in testing their programs. The computer “wasted” time switching from one job to the next, but it paid off in saving programmer time.
Time-sharing terminals were also used for data entry, so we began to see applications in which users, for example, airline reservation clerks entered their own data. Professional keypunch operators began to disappear.
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