microkernel

In computer science, a microkernel is a computer kernel that provides the mechanisms needed to implement an operating system, such as low-level address space management, thread management, and inter-process communication. If the hardware provides multiple privilege levels, then the microkernel is the only software executing at the most privileged level (generally referred to as supervisor or kernel mode). Actual operating system services, such as device drivers, protocol stacks, file systems and user interface code are contained in user space.