The concept was born out of the realization that a single expensive computer could be efficiently utilized by enabling multiprogramming, and, later, by allowing multiple users simultaneous interactive access.
Similarly, small slices of time spent waiting for disk, tape, or network input could be granted to other users.
[note 1] Each user would use their own computer terminal, initially electromechanical teleprinters such as the Teletype Model 33 ASR or the Friden Flexowriter; from about 1970 these were progressively superseded by CRT-based units such as the DEC VT05, Datapoint 2200 and Lear Siegler ADM-3A.
Terminals were initially linked to a nearby computer via current loop or serial cables, by conventional telegraph circuits provided by PTTs and over specialist digital leased lines such T1.
Modems such as the Bell 103 and successors, allowed remote and higher-speed use over the analogue voice telephone network.