The architecture of UNIX is divided into three levels. On the outer crust reside the Application Programs and other utilities. At the heart of UNIX, on the other hand, is the Kernel, which interacts with actual hardware in machine language. The stream lining of these two modes of communication is done by the middle layer called Shell.
Thus the three basic layers are:-
At the core is the physical component of the computer system i.e. the hardware and the central part of UNIX system is Kernel which has record of all the hardware and knows how to communicate with every piece of hardware. The shell is the command interpreter. The uppermost layer consists of users creating the application programs.
The physical component of the computer system is called hardware. In a UNIX, physical components (hardware) are used like as CPU, ALU, main memory (RAM, ROM), I/O devices, external memory (magnetic tapes, CD’s etc).
✓ UNIX SHELL
The shell or the command interpreter is the mediator which interprets the commands we give and then conveys them to the Kernel which ultimately executes them. It provides the user interface to the Kernel. It is basically an expensive program running on the computer all the time and provides an interactive interface between the user and the computer functions. There are three types of shells:-
▪ Bourne Shell
▪ C Shell
▪ Korn Shell
Bourne Shell: - It is the original UNIX Shell written by Steve Bourne and John Mashey from AT & T’s Bell laboratories. It is the standard shell and is available on all UNIX operating system. It is known as “sh”.
C Shell: - It was developed by Bill Joy from university of California. It does not have the programming capabilities of Bourne Shell but is better for interactivity....
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