Mach's IPC model actually got worse on newer machines, as the amount of cycles wasted in some badly thought-out decisions was growing greater. Fortunately other

Mach's IPC model actually got worse on newer machines, as the amount of cycles wasted in some badly thought-out decisions was growing greater. Fortunately other resources make it less visible, so certain things were mitigated (that's how OSF/1 offshoots like Digital Unix and OSX didn't die under its weight), but you could always get a benchmark showing its problems. What Mach really did was strangle the microkernel revolution in the crib by becoming the face of it then turning out to be hilariously slow and giving that reputation to microkernels in general.