Multiprogramming and multitasking programming concepts are familiar to most of us. In a multiprogrammed arrangement several "user programs" can share the use of a single computer in a time sharing mode. An executive program provides the time slices to the "user programs" by activating and deactivating them according to some schedule. When multitasking is added to this arrangement, a "user program" may have several incarnations and the executive provides time slices to the incarnations of the user programs.
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