View source for Time-sharing

'''Time-sharing''' refers to an [[operating system]] which allows the use of a single computer in real time by multiple users at the same time - as opposed to the ealier [[batch]] operating systems, in which users submitted 'jobs', which were run, after which the results (print-out, etc) were returned to them.

With the growth of the [[personal computer]], most computers are no longer used in this way. However, the technical features needed to allow time-sharing (e.g. support for multiple [[process]]es running simultaneously) are such that current OS's are effectively time-sharing OS's. (In fact, some of the most common current ones, such as [[Unix]] and its descendants, such as [[Linux]], started off as actual time-sharing OS's.)

Most time-sharing OS's relied upon hardware features to prevent one user (or process) from interfering with another. These features typically included the provision of two modes for the CPU, a 'user' mode in which users ran, and a 'kernel' or 'executive' mode, used by the OS - the former had restricted capabilities (e.g. it was usually not able to peform I/O operations).

Memory protection (originally, usually [[base and bounds]] [[register]]s) were also used, to prevent a rogue or erroneous used program from damaging other users, or the OS itself. In later machines, [[virtual memory]] included this functionality.

However, it was not essential to have hardware support for time-sharing; in computers which provided only an interpreted language (such as [[BASIC]], in the [[RSTS-11]] OS), the interpreter could keep the users from interfering with each other.