Introduction & Overview
1.1Operating System
An operating system (OS) is a collection of software that manages computer hardware resources and provides common services for computer programs. The operating system is a vital component of the system software in a computer system. Application programs usually require an operating system to function.
1.2Types Of Operating System
a. Real-time
A real-time operating system is a multitasking operating system that aims at
executing real-time applications. Real-time operating systems often
use specialized scheduling algorithms
so that they can achieve a deterministic nature of
behavior. The main objective of
real-time operating systems is their quick and predictable response to events. They have an event-driven or time- sharing design and often aspects of
both. An event-driven system switches between tasks based on their priorities or
external events while time-sharing
operating systems switch tasks based on clock interrupts.
b. Multi-user
A multi-user operating system allows multiple users to access a computer
system at the same time. Time-sharing systems and Internet servers can be
classified as multi-user systems as they
enable multiple-user access to a computer through
the sharing of time. Single-user operating systems have only one
user but may allow multiple programs to run at the same time.
c. Multi-tasking vs. single-tasking
A multi-tasking
operating
system allows
more than
one
program to
be
running at a time, from the point of
view of
human time scales. A single- tasking system
has only one running program. Multi-tasking can be of two types: pre-emptive and co-operative. In pre-emptive multitasking, the operating system slices the CPU time and dedicates one slot to each of
the programs. Unix-like operating systems such as
Solaris and Linux support pre- emptive multitasking, as does AmigaOS. Cooperative multitasking is achieved by relying on each process to give time to the other processes in a defined
manner.
16-bit versions
of Microsoft
Windows
used
cooperative multi-tasking. 32-bit versions of
both Windows NT and Win9x, used pre- emptive multi-tasking. Mac OS prior to OS X used to support cooperative multitasking.
d. Distributed
distributed operating system manages a group of
independent computers and makes them appear to be a single computer. The development of networked
computers that could be linked and communicate with each other gave rise to distributed computing. Distributed computations are carried out on more than one machine. When computers in a group work in
cooperation, they make a distributed system.
e. Embedded
Embedded operating systems are designed to be used in embedded computer systems. They
are designed to operate on small machines like PDAs with less autonomy. They are able to operate with a limited number of resources. They are very compact and extremely efficient by design. Windows CE and Minix
3 are some examples of embedded operating systems.
f. Time-Sharing
Time-sharing operating systems schedule tasks for efficient use of the system and may also include accounting for cost allocation of
processor time, mass storage, printing, and other resources.
1.3 Examples of Operating System
a. UNIX and UNIX-like operating systems
Unix was originally written in assembly language. Ken Thompson wrote B, mainly based on BCPL, based on his experience in the MULTICS project. B was replaced by C, and
Unix, rewritten in C, developed into a large, complex family of inter-related operating systems which have been influential in every modern operating system.
The UNIX-like family is a diverse group of operating systems, with several major sub- categories including System V, BSD, and Linux. The name "UNIX" is a trademark of The Open Group which licenses it for use with any operating system that has been shown
to conform to their definitions. "UNIX-like" is commonly used to refer to the large set of operating systems which resemble the
original UNIX.
Unix-like systems run on a wide variety of computer architectures. They are used heavily
for
servers in
business, as well as workstations in academic and engineering environments. Free UNIX variants, such as Linux and BSD,
are popular in these areas.
Four operating systems are certified
by the The Open
Group
(holder of the Unix trademark) as Unix. HP's HP-UX and IBM's AIX are both descendants of the original System V Unix and are designed to run only on
their respective vendor's hardware. In contrast, Sun Microsystems's Solaris Operating System can run on multiple types of hardware, including x86 and Sparc servers, and PCs. Apple's OS X, a replacement for Apple's earlier (non-Unix) Mac OS, is a
hybrid kernel-based BSD variant derived from NeXTSTEP, Mach, and FreeBSD.
Unix interoperability was
sought by establishing
the
POSIX standard. The POSIX standard can be applied to any operating system, although it was originally created for various Unix variants.
b. Linux and GNU
Linux (or
GNU/Linux) is
a
Unix-like
operating
system
that was
developed without any actual Unix code, unlike BSD and its variants. Linux can be used on a wide range of devices from supercomputers to wristwatches. The Linux kernel is released under an open source license, so anyone can read and modify its code. It has been modified to run on a
large variety of electronics. Although estimates
suggest that Linux is used on 1.82% of all personal computers, it has been widely adopted for use in servers and embedded systems (such as cell phones). Linux has superseded Unix in most places, and is
used on the 10 most powerful supercomputers in the world. The Linux kernel is
used in some popular distributions, such
as Red Hat, Debian,
Ubuntu, Linux Mint
and
Google's Android.
The GNU project is a mass collaboration of programmers who seek to create a completely free and open operating system that was similar to Unix but with
completely original code. It was
started
in 1983
by Richard
Stallman, and is responsible for many of the parts of
most Linux variants. Thousands of
pieces of software for virtually every operating system are licensed under the GNU General Public License. Meanwhile, the Linux kernel began as a side project of Linus Torvalds, a university student from Finland. In 1991, Torvalds began work on it, and posted information about his project on a newsgroup for computer students
and programmers. He received a wave of support and volunteers who ended up creating a full-fledged kernel. Programmers from GNU took notice, and members
of both projects worked to integrate the finished GNU parts with the Linux kernel in order to create a full-fledged operating system.
c. Microsoft Windows
Microsoft Windows
is a family
of proprietary
operating
systems designed by Microsoft Corporation and primarily targeted to Intel architecture based
computers, with an estimated 88.9 percent total usage share on Web connected computers. The newest version is Windows 8 for workstations and Windows Server 2012 for
servers.
Windows 7 recently overtook Windows XP as most used OS.
Microsoft Windows originated in 1985 as an operating environment running on top of
MS-DOS, which was the standard operating system shipped on most Intel architecture
personal computers
at the time.
In 1995, Windows 95
was released which only used
MS-DOS as a bootstrap. For backwards compatibility, Win9x could run real-mode MS-DOS and 16 bit Windows 3.x drivers. Windows ME, released in
2000, was the last version in the Win9x family. Later versions have all
been based on the Windows NT kernel. Current versions of
Windows run on IA-32 and x86-64 microprocessors, although Windows 8 will support ARM architecture. In the
past, Windows NT supported non-Intel architectures.
Server editions of Windows are widely used. In recent years, Microsoft has expended significant capital in an effort to promote the use of Windows as a server operating system. However, Windows' usage on servers is
not
as widespread as on personal
computers, as Windows competes against Linux and BSD for server market share
Anurag
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