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Introduction to Unix Operating System?
If a computer and its peripherals are to be fully utilized, many users should be able to operate simultaneously. In a single user system, resources such as the processor, the printer, hard disc, etc. are kept idling most of the time, since all these resources are at the disposal of a single user. There are many multi-user operating systems in use at that time, normally coded in assembly language, and implemented for specific hardware. To overcome this situation, and to have easy portability of the operating system UNIX was developed. Since a major portion of UNIX is written in C language and only a small portion is coded in assembly language for specific hardware, UNIX became popular for all systems. UNIX can be ported to any system easily. The current trend is that compiler for all high-level languages for any system and for any operating system are written in C. The predominant UNIX-like operating systems which were popular are: AT&T UNIX, SCO UNIX (Santa Cruz Operations), Solaris of Sun Systems, and IRIS of Silicon Graphics for workstations.
 

UNIX FEATURES:
 PORTABILITY
 MACHINE DEPENDENCE
 MULTIUSER OPERATIONS
 HIERARCHIAL FILE SYSTEM
 UNIX SHELL & SHELL PROGRAMMING
 PIPES & FILTERS
 MATURITY
 BACKGROUND PROCESSING
 FILE SECURITY & PROTECTION
 TIME SHARING
 COMMAND INTERPRETATION
 MULTITASKING
 SYSTEM ADMINISTRATION
 COMMUNICATION
 TEXT PROCESSING
 GRAPHICS
 AVAILABILITY OF 4 GLS & RDBMS
 SIMPLE COMMAND STRUCTURE
 JOB ACCOUNTING
 SOFTWARE DEVELOPMENT TOOLS

UNIX STRUCTURE :
Various parts and portion of UNIX is arranged around the hardware. The core of UNIX is the kernel, which schedules jobs and manages data storage, and it is very closely interfaced with hardware. The hardware functions according to the machine instructions released ultimately by the kernel, based on the shell’s interpretation of user commands. Surrounding the shell are parts of software of the shell relating to:

 Execution of commands for piping and filtering actions.
 Tools for carrying out foreground and background processing.
 Utilities for configuring the hardware.
 I/O redirection and command execution utilities.
 Filename substitution.
The shell forms an interface between the user and the kernel. Outside the shell are the different user-specific utilities of UNIX, numbering around 300, which enhance its capability. Above this, are the user programs and application packages, which can facilitate data entry, data modification, query, report generation, etc. The shell is a program that collects and interprets the user commands, invokes the concerned program file from memory and directs the kernel to execute them.
Externally, the UNIX operating system is made up of two parts. One part is large set of system programs, each one corresponding to a command, and another part of the shell, which interprets, manages and coordinates the execution of these programs. The user sees the shell command as one peculating down the UNIX system, and the kernel, looking up to the user through the shell for the next set of process. separate shell process is apportioned to each user. The separate shell once created provides an environment within which the user operates. The shell environment consists of the following to ensure proper interaction between the user and the system :-

 

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