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Time SharingTime sharing utilizes multitasking for the purpose of sharing a high performance computer among several users (or batch jobs) at the same time. In general, tasks run largely independently of each other in time sharing systems. Therefore, inter-task communication is only offered in a simple fashion. One of the most popular time sharing systems is Unix. It was developed when the processing power of the available computer was smaller than that needed for the job. Consequently, the multitasking system had to share the scarce resource "processing power" as "fairly" as possible among competing tasks. However, it should be noted that system throughput is usually degraded by multitasking in such systems, because the scheduling overhead is significant. Under Unix, for example, it is possible that two compute-bound programs each runs a minute when it is the only program running; however, running in parallel, they would need 2.5 minutes. Parallel processing may be more fair (User 1 and User 2 have to wait equally long for their job to finish), but is usually less efficient.
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