An Operating System is a collection of programs that
provides an interface between application programs and the computer system
(hardware). Its primary function is to provide application programmers with an
abstraction of the system resources, such as memory, input-output and
processor, which enhances the convenience, efficiency and correctness of their
use.
These programs or functions within the OS provide various kinds of
services to the application programs. The application programs, in turn, call
these programs to avail of such services. Thus the application programs can
view the computer resources as abstract entities, (for example a block of
memory can be used as a named sequential file with the abstract Open, Close,
Read, Write operations) without need for knowing the low level hardware details
(such as the addresses of the memory blocks). To get a better idea of such
services provided by the OS, the user may like to refer to the DOS services for
the IBM PC Compatibles.
The
natural way to view computation in a typical modern computer system is in the
form of a number of different programs, all of which, apparently, run in
parallel. However, very often, all the programs in the system are executed on a
single physical CPU or processor. Each program runs for a small continuous
duration at a time, before it is stopped and another program begins to execute.
If this is done rapidly enough, it appears as if all programs are running
simultaneously. These programs very often perform independent computations,
such as the programs executing in different windows on a PC. In real time
systems, most often, such programs cooperate with each other, by exchanging
data and synchronizing each other’s execution, to achieve the overall
functionality and performance of the system.
Types
of Operating Systems
•
Stand-Alone Operating systems
•
Network Operating systems
•
Embedded Operating Systems
1-Stand-Alone
Operating System
It
is a complete operating system that works on a desktop or notebook computer.
Examples
of stand-alone operating systems are:
•
DOS
•
Windows 2000 Professional
•
Mac OS X
2-Network
Operating System
It
is an operating system that provides extensive support for computer networks. A
network operating system typically resides on a server. Examples of a network
operating system are:
•
Windows 2000 Server
•
Unix
•
Linux
•
Solaris
3-Embedded
Operating System
It
can be find this operating system on handheld computers and small devices, it
resides on a ROM chip. Examples of embedded operating systems are:
•
Windows CE
•
Pocket PC 2002
•
Palm OS
The
above classification is based on the computing hardware environment towards
which the OS is targeted. All three types can be either of a real-time or a non-real-time
type. For example, VxWorks is an RTOS of the first category, RT-Linux and ARTS
are of the second category and Windows CE of the third category.
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