What is the difference between user mode and kernel mode in NT 4.0?
User mode is restricted from accessing hardware directly. This is where all user applications are executed. The kernel mode has direct access to hardware and maintains control over all resources and the system itself. The central or core elements of the operating system are part of the kernel mode.
These two modes correspond to the theory or concept of protection rings for an operating system. Kernel mode represents RING 0, which has the highest level of access and controls the environment. User mode represents RING 3, which is the lowest level of access and which must request access to resources from the lower numbered levels. The levels are exactly the same for Windows 2000.