That hasn’t aged well because the microkernels of the day like Mach failed to keep their promises. There are newer ones like the L4 family that were designed sp

That hasn’t aged well because the microkernels of the day like Mach failed to keep their promises. There are newer ones like the L4 family that were designed specifically for performance, but they have not been deployed as a base for a full-featured OS like Mach was for macOS or OSF/1, where IPC was too slow and the OS server was glommed to the microkernel, making it an even ungainlier monolith. Just another illustration of academic theory vs industrial practices.