Microkernel

Microkernel is a kernel that includes a minimum amount of software that can provide what operating systems provide, such as address space, thread management, and inter-process communication. Just enough to run the most basic functions of a system.

This provides implementation flexibility so it allows other parts to be implemented efficiently since it does not impose a lot of policies.

It is extendable. If any new services are to be added they are added to user address space and hence requires no modification in kernel space.

Other operations are done outside of the kernel, in user space. Therefore, the operating system is unaffected as user services and kernel services are isolated, so if any user service fails it does not affect kernel service.

Since the kernel is small in microkernel implementations, it requires less time to load compared to monolithic systems.