Purpose of an Operating
System:
The OS acts like a translator between user applications and
the hardware. A user interacts with the computer system through an application,
such as a word processor, spreadsheet, computer game or instant messaging
program. Application programs are designed for a specific purpose, such as word
processing, and know nothing of the underlying electronics. For example, the
application is not concerned with how information is entered into the
application from the keyboard. The operating system is responsible for the
communication between the application and the hardware.
When a computer is powered on, it loads the OS, normally
from a disk drive, into RAM. The portion of the OS code that interacts directly
with the computer hardware is known as the kernel. The portion that interfaces
with the applications and user, is known as the shell. The user can interact
with the shell using either the command line interface (CLI) or graphical user
interface (GUI).
When using the CLI, the user interacts directly with the
system in a text-based environment by entering commands on the keyboard at a
command prompt. The system executes the command, often providing textual
output. The GUI interface allows the user to interact with the system in an
environment that uses graphical images, multimedia, and text. Actions are
performed by interacting with the images on screen. GUI is more user friendly
and requires less knowledge than CLI of the command structure to utilize the
system. For this reason, many individuals rely on the GUI environments. Most
operating systems offer both GUI and CLI.
OS Requirments!!
There are many different operating systems available. The
major groupings are listed here with some examples.
Microsoft Windows: XP, Vista, 2003 Server
UNIX-Based: IBM AIX, Hewlett Packard HPUX, and Sun Solaris
BSD - Free BSD
Linux-Based (Many varieties)
Macintosh OS X
Non-Unix Proprietary: IBM OS/400, z/OS
While most of these operating systems require the user to
purchase and agree to a commercial license, there are several operating systems
released under a different type of licensing scheme known as the GNU Public
License (GPL).
Commercial licenses usually deny end-users the ability to
modify the program in any way. Windows XP, Mac OS X and UNIX are all examples
of commercial OS software.
In contrast, the GPL allows end-users to modify and enhance
the code, if they desire, to better suit their environment. Some common
operating systems, which are released under the GPL, include Linux and BSD.
OS Installation
Methods:
An OS is installed in a defined section of the hard disk,
called a disk partition. There are various methods for installing an OS. The
method selected for installation is based on the system hardware, the OS being
installed, and user requirements. There are four basic options available for
the installation of a new OS:
Clean Install:
A clean install is done on a new system or in cases where no
upgrade path exists between the current OS and the one being installed. It
deletes all data on the partition where the OS is installed and requires
application software to be reinstalled. A new computer system requires a clean
install. A clean install is also performed when the existing OS installation
has become damaged in some way.
Upgrade:
If staying within the same OS platform, it is often possible
to do an upgrade. With an upgrade, system configuration settings, applications
and data are preserved. It simply replaces the old OS files with the new OS
files.
Multi-boot:
It is possible to install more than one OS on a computer to
create a multi-boot system. Each OS is contained within its own partition and
can have its own files and configuration settings. On start-up, the user is
presented with a menu to select the desired OS. Only one OS can run at a time
and it has full control of the hardware.
Virtualization:
Virtualization is a technique that is often deployed on
servers. It enables multiple copies of an OS to be run on a single set of
hardware, thus creating many virtual machines. Each virtual machine can be
treated as a separate computer. This enables a single physical resource to
appear to function as multiple logical resources.
