Unix
Unix is an operating system that was developed by Kenneth Thompson and colleagues at AT&T Bell Laboratories in the late 1960's. The program was originally intended for scientists and engineers, although its use has expanded since the inception of Unix. There are now several modifications to the AT&T standard, mostly because Bell Labs distributed the operating system in its source language form. This allowed anyone to modify the system for his or her own purposes. Now, Unix is the operating system on which many network protocols, such as TELNET and FTP, are based.
There are two main types of Unix. System V is produced by AT&T and BSD4.1- 4.3 are produced by The University of California at Berkeley.
Operating systems, including Unix, determine how a computer is to operate, and provide the link between the user and the computer resources. An operating system schedules tasks and allocates computer resources, including hardware such as the central processing unit, system memory, disk and tape storage systems, printers, terminals, modems, and any other internal or external peripheral.
The core of Unix is called the kernel. The kernel is responsible for the allocation of resources and the management of the memory. The software connection between the user and the kernel is called the shell. There are several different shells in Unix systems, the most popular being the Cshell. Part of Unix's appeal and power is the generic nature of this operating system, which makes Unix independent of the language of the machine itself. It can run on virtually any computer equipped with a C compiler. A drawback to the more widespread popularity of Unix concerns the arcane nature of its command language and its general lack of user friendliness. These aspects reflect the origin of Unix--a system intended for a small cadre of specialists for whom the system's eccentricities posed no disadvantage. Now, Unix is adapting to a wider audience, with the development of graphical user interfaces such as MOTIF.
Another generic aspect of operating systems is their ability to perform a myriad of functions at the same time, staging these tasks so that the CPU is working on only one task at any particular time. Unix was designed to provide another level of multi-tasking capability. It was designed as a multi-user operating system, which allows more than one person to use the computer resources at the same time, and share resources with the other users on the system.
The multi-user nature of Unix is reflected by the login procedure, which typically requires a user to supply a name and a password. This allows users to differentiate their files from those of others. A Unix file is a collection of information, usually in text format, that is saved under a filename. Files are organized in a file system consisting of directories, which in turn are arranged under other directories, and so on. The organization has a tree structure. Related files can be grouped together in a common directory. An analogy for the organization of the files is a conventional file cabinet. The cabinet itself represents the main directory, the drawers represent subdirectories, the file folders in the drawers represent further subdirectories, and the actual report represents the file.
From its inception until about 5 years ago, Unix's popularity was centered principally around workstations--computers devoted to high-end computational tasks such as engineering computer-aided design, desktop publishing, manufacturing control, laboratory simulations, telephone communications, and software development. Now, the emergence of the Unix-based operating program called Linux is increasing the popularity of Unix for personal computers.
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