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The chip that runs programs by repeating fetch-decode-execute billions of times per second.
The processor: fetches instructions from memory, decodes them, and executes them. Modern CPUs have multiple cores and pipeline many instructions in parallel. Clock speed (GHz) is only one factor in real performance.
An out-of-order superscalar core with branch prediction, speculative execution, and multi-level caches. Instructions retire in program order but execute in any order the dependencies allow. IPC (instructions per cycle) varies wildly with workload locality.