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The operating system provides an interface between an application program and the computer hardware, so that an application program can interact with the hardware only by obeying rules and procedures programmed into the operating system. The operating system is also a set of services which simplify development and execution of application programs.
An example would be from supervisor mode to protected mode. This is where the operating system performs actions like accessing hardware devices or the memory management unit. Generally the operating system provides a library that sits between the operating system and normal user programs. Usually it is a C library such as Glibc or Windows API ...
For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between programs and the computer hardware, [1] [2] although the application code is usually executed directly by the hardware and frequently makes system calls to an OS function or is interrupted by it.
An operating system is the low-level software that supports a computer's basic functions, such as scheduling processes and controlling peripherals. [ 122 ] In the 1950s, the programmer, who was also the operator, would write a program and run it.
In computing, a shell is a computer program that exposes an operating system's services to a human user or other programs. In general, operating system shells use either a command-line interface (CLI) or graphical user interface (GUI), depending on a computer's role and particular operation. It is named a shell because it is the outermost layer ...
A kernel is the core part of the operating system that defines an application programming interface for applications programs (including some system software) and an interface to device drivers. Device drivers and firmware , including computer BIOS or UEFI , provide basic functionality to operate and control the hardware connected to or built ...
The operating system keeps its processes separate and allocates the resources they need, so that they are less likely to interfere with each other and cause system failures (e.g., deadlock or thrashing). The operating system may also provide mechanisms for inter-process communication to enable processes to interact in safe and predictable ways.
In OS/360 and descendant systems, the (privileged) operating system facility is called IEWFETCH, [2] and is an internal component of the OS Supervisor, whereas the (non-privileged) LOADER application can perform many of the same functions, plus those of the Linkage Editor, and is entirely external to the OS Supervisor (although it certainly ...