UNIX
Operating System Concept
U.Y: 1435/1436 H
What is an Operating System?

The operating system (OS) is the program which starts
up when you turn on your computer and runs
underneath all other programs - without it nothing would
happen at all.

In simple terms, an operating system is a manager. It
manages all the available resources on a computer, from
the CPU, to memory, to hard disk accesses.
What is an Operating System?
•
Tasks the operating system must perform:
•
Control Hardware - The operating system controls all the parts of
the computer and attempts to get everything working together.
•
Run Applications - Another job the OS does is run application
software. This would include word processors, web browsers, games,
etc...
•
Manage Data and Files - The OS makes it easy for you to
organize your computer. Through the OS you are able to do a
number of things to data, including copy, move, delete, and rename it.
This makes it much easier to find and organize what you have
General Characteristics of UNIX as an
Operating System (OS)

Multi-user & Multi-tasking - most versions of UNIX are capable
of allowing multiple users to log onto the system, and have each run
multiple tasks.This is standard for most modern OSs.

Over 30 Years Old - UNIX is over 30 years old and it's popularity
and use is still high. Over these years, many variations have spawned
off and many have died off, but most modern UNIX systems can be
traced back to the original versions. It has endured the test of time.
For reference, Windows at best is half as old (Windows 1.0 was
released in the mid 80s, but it was not stable or very complete until
the 3.x family, which was released in the early 90s).
General Characteristics of UNIX as an
Operating System (OS)
•
Large Number of Applications – there are an enormous
amount of applications available for UNIX operating systems.
They range from commercial applications such as CAD, Maya,
WordPerfect, to many free applications.
•
Free Applications and Even a Free Operating System of all of the applications available under UNIX, many of them
are free. The compilers and interpreters that we use in most of
the programming courses here at UMBC can be downloaded
free of charge. Most of the development that we do in
programming courses is done under the Linux OS
General Characteristics of UNIX as an
Operating System (OS)
•
Less Resource Intensive - in general, most UNIX
installations tend to be much less demanding on system
resources. In many cases, the old family computer that can
barely run Windows is more than sufficient to run the latest
version of Linux.
•
Internet Development - Much of the backbone of the
Internet is run by UNIX servers. Many of the more general web
servers run UNIX with the Apache web server - another free
application.
OS Organization
Unix Components

As with most modern operating systems, the Unix OS is also
made up of many different components.

In a very general sense, Unix is divided into two main
components, kernel and utilities.

The kernel, which is critical to the operation of the OS, is
loaded into Random Access Memory (RAM) by the boot
loader, where it remains memory resident for as long as the
machine remains powered on.

The utilities are programs which (typically) reside on a disk
device (e.g. a hard drive).
Unix Components
 Unix
is comprised of three main components:
 Kernel

Shell
 Utilities
or Programs
Unix Components

Kernel - The core of the UNIX system. Loaded at system
start
up
(boot). Memory-resident
control
program.
Manages the resources of the system, presenting them to
you and every other user as a coherent system.
Provides service to user applications such as device
management, process scheduling,
Unix Components

Example functions performed by the kernel are:

managing the machine's memory and allocating it to each
process.

scheduling the work done by the CPU so that the work of
each user is carried out as efficiently as is possible.

accomplishing the transfer of data from one part of the
machine to another

interpreting and executing instructions from the shell
enforcing file access permissions
Unix Components

•
Example functions performed by the kernel are:
managing the machine's memory and allocating it to each
process.
•
scheduling the work done by the CPU so that the work of
each user is carried out as efficiently as is possible.
•
accomplishing the transfer of data from one part of the
machine to another
•
interpreting and executing instructions from the shell
enforcing file access permissions
Unix Components
•
You do not need to know how the kernel is implemented in
order to use a UNIX system (in this class anyway).
Unix Components

Shell - a command interpreter - Whenever you login to a
Unix system, Unix opens an environment for you. This
environment is actually a shell program. Your shell is
independent of other user's shell environment

The shell's prompt is usually visible at the cursor's
position on your screen. To get your work done, you
enter commands at this prompt.
Unix Components

The shell is a command interpreter; it takes each
command and passes it to the operating system kernel to
be acted upon. It then displays the results of this
operation on your screen.

Several shells are usually available on any UNIX system,
each with its own strengths and weaknesses.
Unix Components

Utilities or Programs - UNIX provides several hundred utility
programs, often referred to as commands or applications.

Standard Unix commands are available to allow the user to
accomplish universal functions
− editing
− file maintenance
− printing
− sorting
− programming support
− view online info
Unix Organization
Link:
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