user mode

In computer science, hierarchical protection domains, often called protection rings, are a mechanism to protect data and functionality from faults (fault tolerance) and malicious behaviour (computer security). This approach is diametrically opposite to that of capability-based security.Computer operating systems provide different levels of access to resources. A protection ring is one of two or more hierarchical levels or layers of privilege within the architecture of a computer system. This is generally hardware-enforced by some CPU architectures that provide different CPU modes at the firmware level. Rings are arranged in a hierarchy from most privileged (most trusted, usually numbered zero) to least privileged (least trusted, usually with the highest ring number). On most operating systems, Ring 0 is the level with the most privileges and interacts most directly with the physical hardware such as the CPU and memory.
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For the use of "user space" in Wikipedia, see Wikipedia:User page A protected mode operating system usually segregates virtual memory into kernel space and user space. Kernel space is strictly reserved for running the kernel, device drivers and kernel extensions. In most operating systems, kernel memory is never swapped out to disk. In contrast, user space is the memory area where all user mode applications work and this memory can be swapped out when necessary. The term userland is often used for referring to operating system software that runs in user space.
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