macOS doesn’t work like it used to. With heuristic task dispatching and sensitivity to factors like quality of network service, troubleshooting can get fiendishly difficult.
cores
A modern iPod has a faster and more capable processor than the original Mac. How have they got so much faster? A look at CPUs, GPUs, and more.
Designing algorithms which can benefit from multiple cores and GPUs is not only non-trivial, it remains desperately difficult for humans.
The Eclectic Light Company 