Early Operating Systems

Computers of the 1950s could perform only one job or task at a time. This is often called single-user batch processing. The computer runs one program at a time while processing data in groups or batches. In these early systems, users generally submitted their jobs to a computer center on decks of punched cards and often had to wait hours or even days before printouts were returned to their desks. Computers were very large (often filling entire rooms) and expensive (often costing millions of dollars). Personal computers did not exist; people did not have computers at their desks and in their homes.

Software systems called operating systems were developed to make using computers more convenient. Early operating systems smoothed and speeded up the transition between jobs, increasing the amount of work, or throughput, computers could process.

As computers became more powerful, it became evident that single-user batch processing was inefficient, because so much time was spent waiting for slow input/output devices to complete their tasks. It was thought that many jobs or tasks could share the resources of the computer to achieve better utilization. This is achieved by multiprogrammingthe simultaneous operation of many jobs that are competing to share the computer's resources. With early multiprogramming operating systems, users still submitted jobs on decks of punched cards and waited hours or days for results.

In the 1960s, several groups in industry and the universities pioneered timesharing operating systems. Timesharing is a special case of multiprogramming in which users access the computer through terminals, typically devices with keyboards and screens. Dozens, or even hundreds, of users share the computer at once. The computer actually does not run the users' jobs simultaneously. Rather, it runs a small portion of one user's job, then moves on to service the next user, perhaps providing service to each user several times per second. Thus, the users' programs appear to be running simultaneously. An advantage of timesharing is that user requests receive almost immediate responses.