Operating system
The term operating system (OS) is most often used colloquially to mean all the software that "comes with" a computer system before any applications are installed.
In traditional operating systems, the OS is the system software responsible for the direct control and management of the hardware that makes up a computer and basic system operations such as
- memory management
- process management
- file management
- input/output management
The design of an operating system uses a monolithic kernel, microkernel or exokernel approach. Among commercial systems, such as Unix and Windows, the monolithic approach is predominant, with a few noted exceptions (eg, QNX). The microkernel approach is more popular among research OSes.
Operating systems which distinguish more than one user also track such things as file ownership (I can't read (or erase or alter) your files unless you allow me to) and access to the machine (without properly identifying myself, the operating system will not let me run programs, including itself). These restrictions on users' privileges necessarily require creation of a kind of superuser who can tell the system about newly authorized users, revoke privileges for formerly authorized users, permit those who have forgotten their passwords access, install software, delete software, ...
Classifications and Terminology
monolithic kernel -- microkernel -- exokernel
real-time operating system -- time-share -- multitasking -- embedded -- single-user -- multi-user
asymmetric and symmetric multiprocessing (SMP) -- clustering -- distributed computing
orthogonally persistent -- capabilities versus access control lists
object-oriented operating system
See also history of operating systems, which contains a list of operating systems.
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