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This article covers theevolution of time-sharing systems, providing links to major earlytime-sharing operating systems, showing their subsequent evolution.

The meaning of the termtime-sharing has shifted from its original usage. From 1949 to 1960, time-sharing was used to refer to multiprogramming; it evolved to mean multi-user interactive computing.

Time-sharing was first proposed in the mid- to late-1950s and first implemented in the early 1960s. The concept was born out of the realization that a single expensive computer could be efficiently utilized by enablingmultiprogramming, and, later, by allowing multiple users simultaneousinteractive access.^[1] Years laterChristopher Strachey wrote he considered the change in the meaning of the termtime-sharing to be a source of confusion and not what he meant when he wrote his original paper in 1959.^[2][3]

Without time-sharing, an individual user would enter bursts of information followed by long pauses; but with a group of users working at the same time, the pauses of one user would be filled by the activity of the others. Similarly, small slices of time spent waiting for disk, tape, or network input could be granted to other users. Given an optimal group size, the overall process could be very efficient.^{[note 1]}

Each user would use their owncomputer terminal, initially electromechanicalteleprinters such as theTeletype Model 33 ASR or theFriden Flexowriter; from about 1970 these were progressively superseded byCRT-based units such as theDECVT05,Datapoint 2200 andLear SieglerADM-3A.

Terminals were initially linked to a nearby computer viacurrent loop orserial cables, by conventionaltelegraph circuits provided byPTTs and over specialist digitalleased lines suchT1.Modems such as theBell 103 and successors, allowed remote and higher-speed use over theanalogue voice telephone network.

See details and additional systems in the table below. Relationships shown here are for the purpose of grouping entries and do not reflect all influences. The Cambridge Multiple-Access System^[6][7] was the first time-sharing system developed outside the United States.

• History of CP/CMS has many period details and sources.
• Timeline of operating systems

• History of software
• Time-sharing operating systems

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