In conventional multi-core processors, like the Intel CPUs used in previous Mac models, all cores are the same. Allocating threads to cores is therefore a matter of balancing their load, in what’s termed symmetric multiprocessing (SMP).
In Activity Monitor’s CPU History window, core load (as CPU %) is shown against time, with the oldest values at the left. Odd-numbered cores in the left half are real, and show the eight cores in the 8-Core Intel Xeon W under heavy load. Even-numbered cores in the right half are the virtual cores of Hyper-threading, engaged to cope with the heaviest load.
CPUs in Apple Silicon chips are different, as they contain two different core types, one designed for high performance (Performance, P or Firestorm cores), the other for energy efficiency (Efficiency, E or Icestorm cores). For these to work well, threads need to be allocated by core type, a task which can be left to apps and processes, as it is in Asahi Linux, or managed by the operating system, as it is in macOS. This article explains how macOS manages core allocation in all Apple’s M1 series chips, in what it terms asymmetric multiprocessing (AMP, although others prefer to call this heterogeneous computing).
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