User mode refers to two similar concepts in computer architecture. In CPU design, a user mode is a nonprivileged state where the executing code is forbidden by the hardware from performing certain operations (such as writing to memory not assigned to it) which could destabilize the system or constitute a security hole. In operating system design, user mode is an analogous nonpriviliged execution mode where the running code is forbidden by the kernel from performing potentially dangerous operations such as writing to system configuration files, killing other users' processes, rebooting the system, etc. Jump to: navigation, search Computer architecture is the theory behind the design of a computer. ... Jump to: navigation, search [To a large extent, the design of a CPU, or central processing unit, is the design of its control unit. ... Jump to: navigation, search In computing, an operating system (OS) is the system software responsible for the direct control and management of hardware and basic system operations. ... It has been suggested that Microkernel be merged into this article or section. ... In computing, a process is a running instance of a program, including all variables and other state. ...

User mode in CPU design

User mode does not allow the program to access certain privileged operations of the processor in order to protect the operating system from crashing. Each application that runs in user mode runs in its own protected user space, and is not able to access any other application's user space.

The x86 architecture is unusual in having four privilege levels, of which the most privileged, ring 0 (zero), is treated as kernel mode. The least privileged is ring 3, usually treated as user mode. Rings 1 and 2 are rarely used. x86 or 80x86 is the generic name of a microprocessor architecture first developed and manufactured by Intel. ... Rings 1 and 2 are rarely used privilege levels in which an x86 processor can operate between the normal Ring 0 (kernel mode) and Ring 3 (user mode). ...

User mode in operating system design

User mode refers to the normal privilege level of an operating system that implements separation of privileges; that is, the ordinary level which is opposed to the special privileged superuser or administrative level (called "root" on Unix-style systems.) Every process started in user mode on such a system is granted and denied certain privileges, usually based on those assigned to a logged-in user who started the process. On many computer operating systems, superuser is the term used for the special user account that is controlled by the system administrator. ... Jump to: navigation, search It has been suggested that List of Unixes be merged into this article or section. ...

An operating system's user mode is typically (though not necessarily) implemented by running code in user mode on the underlying CPU to gain hardware-level protection from inadvertent or malicious attempts to access another process' memory. User mode at the operating system level entails a much more complex set of permissible actions than what is provided at the CPU level, though; for example, by default on Unix systems, code running in user mode is not allowed to mimic a well-known service by listening on ports below 1024, while code running in superuser mode is. Jump to: navigation, search It has been suggested that List of Unixes be merged into this article or section. ... In computing, a port (derived from seaport) is usually a connection through which data is sent and received. ... On many computer operating systems, superuser is the term used for the special user account that is controlled by the system administrator. ...

See also

• User mode Linux