Second, preemption isn’t free. Every time you switch tasks, you pay a price, known in computer science as a context switch. When a computer processor shifts its attention away from a given program, there’s always a certain amount of necessary overhead. It needs to effectively bookmark its place and put aside all of its information related to that program. Then it needs to figure out which program to run next. Finally it must haul out all the relevant information for that program, find its place in the code, and get in gear. None of this switching back and forth is “real work”—that is, none of
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