Operating System Concepts || Operating System || Bcis Notes

Operating System Concepts

An operating system concepts is basically a collection of software that manages computer hardware resources and provides common services for computer programs. Operating system is a crucial component of the system software in a computer system.

The operating system has following concepts.

 Process:

• A process is an instance of a program in execution.
• A program becomes process when executable file is loaded in the main memory.
• It is defined as an entity that represents the basic unit of work to be implemented in the system.

 Files:

• A file is a named collection of related information that is recorded on secondary storage such as magnetic disks, magnetic tapes, and optical disks.
• In general, a file is a sequence of bits, bytes, lines or records whose meaning is defined by the files creator and user.

 System Calls:

• In computing, a system call is a programmatic way in which a computer program requests a service from the kernel of the operating system it is executed on.
• A system call is a way for programs to interact with the operating system. A computer program makes a system call when it makes a request to the operating system’s kernel.
• System call provides the services of the operating system to the user programs via Application Program Interface(API).
• It provides an interface between a process and operating system to allow user-level processes to request services of the operating system. System calls are the only entry points into the kernel system. All programs needing resources must use system calls.

The Shell:

The shell is the outermost layer of the operating system. Shells incorporate a programming language to control processes and files, as well as to start and control other programs. The shell manages the interaction between you and the operating system by prompting you for input, interpreting that input for the operating system, and then handling any resulting output from the operating system.

Shells provide a way for you to communicate with the operating system. This communication is carried out either interactively (input from the keyboard is acted upon immediately) or as a shell script. A shell script is a sequence of shell and operating system commands that are stored in a file.

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