Real systems rarely can pass idealistic academic ideals. Balancing benefits and costs of microkernel and monolithic kernels is common. It looks like Google SE

Real systems rarely can pass idealistic academic ideals. Balancing benefits and costs of microkernel and monolithic kernels is common. It looks like Google SEO gaming by removal of old content is making it hard to find good sources, but look at how OS/2 used ring 2 if you want to know. Message passing and context switching between kernel and user mode is expensive, and if you ever used NT 3.51 that was clearly visible as were the BSoDs when MS shifted to more of a 'hybrid' model.