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Unformatted text preview: supplied by DEC (Digital Equipment Coporation) is called Ultrix, and
Unix supported on systems supplied by HP (Hewelett Packard) is called HP-Unix.
Structure of Unix
The Unix operating system is structured in the following three layers:
1. Kernel. This layer has all the modules for process, memory, file, device, and
Shell. This layer has the command interpreter. Unix basically provides a
command-line interface (some vendors have added GUI to their new versions of
Unix). There are a large number of very useful commands provided by the shell.
Every command is designed to do a single, very specific task. To do larger, more
complex tasks, users can easily combine several commands in the form of a shell
script to produce exactly the result they want. The shell script can even be stored
in a file, which can be made an executable file, which when executed will act like
a new shell command.
An interesting service provided by the shell layer is called pipe, which allows
users to send the output of one program to the input of another program without
storing the output of the first program in a temporary file. For example, entering:
invokes the command who, which displays the names of all currently logged in
users, and pipes its output to sort. The result is a sorted list of currently logged in
users. A pipeline is a connection of two or more programs through pipes. The
length of a pipeline can be arbitrarily long, and the programs used in forming
pipelines are called filter programs (or just filters) because they act as data filters,
transforming the data passed on to the next program in the pipeline.
3. Utilities. This layer has all the OS capability enhancement software including
language compilers, text editors, text processing programs, and a wide variety of
utilities and tools. Over the years, a rich set of very powerful tools has been added to this layer, which allows effective program development and system
management. Because of this, Unix is often referred to by many...
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This document was uploaded on 04/07/2014.
- Spring '14