Operating Systems : Multi-User

Multi-user operating systems are used on large mainframe computers. A mainframe computer system has one very powerful processing unit which may contain many microprocessors. Many users will all share this processing unit. They use terminals (a keyboard and a monitor) to access the mainframe computer.

A multi-user operating system lets more that one user work on a mainframe computer at the same time.

A multi-user operating system allocates the CPU time of the mainframe computer between the different users. Each user in turn is given a small time slice of the CPU time. Because these time slices are very small the users believe that they are all using the mainframe at the same time.

This diagram shows how a mainframe computer with four terminals connected to it divides its processing time up.

Time can be shared equally between each user or can be allocated to users using a priority system so that some users get more time than others. Multi-user operating systems rely on having very powerful mainframe computers to process data.

GCSE ICT Companion 04 - (C) P Meakin 2004