In a single user system such as MS-DOS, the user has all of the computer system available all of the time. In a multiuser system, resources must be shared with many users. This is accomplished by giving one user the entire resources of the system for a short time, then stopping the job in process, saving the current state of the job, loading another user’s job, and continuing. Some time later, the first user’s job is recalled and processed a bit more. Eventually, each user’s job gets done.
Slicing up the CPU time and dividing it among several users is called time sharing. Management of the CPU and each user’s job is called scheduling.
Information about each process, user, or job is stored in a PIB. Along with the PIB is a PCB, which contains the current state of the job in progress. All the jobs (pibs) wait in line to be processed. This line is a queue, similar to the checkout line at the supermarket.
See Also