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Priya clicked the link and nothing happened . The tab sat there , grey and patient , and she had time to resent it . Then the page arrived all at once , as if the wait had been imaginary . She wanted to know which of those two moments was the lie . " Neither , " said her housemate , Jonah , without looking up from his own screen . " The chip was busy the whole time . It just was not busy in a way you can see . " The chip he meant was the CPU , the central processing unit . Priya had thought of it as a very fast calculator . Jonah shook his head . " It does calculate . Most of the time it is also deciding where a number lives , what to do next , and what it can safely guess . " He held up a finger , one instruction , the smallest job . " The processor fetches that instruction from memory . Then it decodes it , which only means it works out what is being asked . Then it executes it , and lines up the next one . People call that fetch , decode , execute . A real chip does not do those steps like a polite queue . It can have several instructions in overlapping stages . If a program reaches a fork , do this if something is true , otherwise do that , the CPU may guess which path is coming , and sometimes it starts the work before it is sure . Waiting is the expensive part . A wrong guess gets thrown away . A right guess means the page does not have to stall for that decision . " Priya asked what the guess was made of . Jonah tapped the case of the laptop , not the picture on the screen . " Transistors . Tiny switches that control an electrical signal , and that signal can stand for one of two states , the binary the machine actually uses . A modern chip can hold billions of them . Switches are not a plan . The plan is which instruction is ready , which branch was predicted , and whether the work can be split . A chip may have several cores , several workers side by side , but the program has to be written so that job can actually be shared . If it cannot , the extra cores may not help that particular job . " The page on Priya's screen had a photo now , and the line of text she had wanted . The computer had not understood her . It had fetched , compared , moved , and decided , over and over , faster than the resentment . " So fast is not one trick , " she said . " No , " said Jonah . " It is a lot of small decisions that happened to finish before you got annoyed . "
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