Write about Operating System (OS) and its types?

Operating System (OS)

An operating system is a collection of programs which controls the overall operation of a computer. The operating system acts as an intermediary between the user and computer. The role of operating system is similar to the head of the family or a manager of a company. The key functions of Operating System are :

1. It provides an environmenr in which users and application software can do work.
2. It manages different resources of the computer like the CPU time, memory spacec, file storage, I/O devicces etc. During the use of coputer by other programs or users, operating system manages various resources and allocates them whenever required, efficiently.
3. It controls the execution of different programs to prevent occurance of error.
4. It provides a convenient interface to the use in the form of commands and graphical interface, which facilitates the use o computer.

Some available operating systems are WINDOWS 7, Windows XP, Linux, Mac OS X Snow Leopard, Microsoft Disk Operating System (MS-DOS).

Lets discuss some popular OS

UNIX

Unix  is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, development starting in the 1970s at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and others. It was  the first operating  system  to be written  in a high-level  language,  C.

MS-DOS

MS DOS was develop by Microsoft Inc. in 1981 and has been the most widely used operating systems of IBM compatible microcomputers. Because  of its popularity,  Microsoft  later took a decision  to launch  independently   Microsoft  Windows  operating  system  in 1990s.

Stucture of MS DOS

MS DOS  is partitioned into m any layers. These layers segregate the kernel logic of the operating system the user’s idea of the system, from the hardware on which it is being run. These layers are :

i.BIOS (basic input/output system)

ii.DOS kernel

iii. Command Processor (Shell)

i.BIOS

Every computer system comes with its own copy of BIOS. The manufacturer of the comuter system provides it. It holds the default resident hardware dependent drivers for the following device :

• Console display and keyboard (CON)
• Date and time
• Line Printer (PRN)
• Boot disk device (Clock Device)
• Auxiliary device (Aux)
• Microsoft Windows

ii. DOS kernel

The DOS kernel is most used by application programs. It is provided by Microsoft Corporation itself and contains large number of hardware independent service. These services are called system functions. It performs following functions:

• File management
• Record management
• Memory management
• Character device input/output
• Access to the real time clock

iii. Command processor

One of the fundamental tasks of a shell is to load a program into memory on request and pass control of the system to the program so that the program can execute. When the program terminates, control returns to the shell, which prompts the user for another command. In addition, shell usually includes functions for file and directory maintenance and display. In theory, most of these functions could be provided as programs, but making them resident in the shell allows them to be accessed more quickly. The tradeoff is memory space versus speed and flexibility. Early microcomputer based operating systems provided a minimal number of resident shell commands because of the limited memory space; modern operating systems such as MS-DOS include a wide variety of these functions as internal commands.

Microsoft Windows

Microsoft   Windows  operating   system  was  developed   by Microsoft   to  overcome  the  limitations  of  its own  MS- DOS  operating   system.   Firstsuccessful     version  of this  operating   system  was  Windows   3.0,  released   in  1990. Subsequently   released  versions  were  Windows   95,  Windows   98,  Windows   2000,  Windows   XP,  Windows   XP Professional,   and Windows  Vista. The numbers  associated  with  some of these  released  versions  indicate  their year of release.  It is a single-user,  multitasking   operating  system.  That  is, a user may run more than  one program  at a time.

Microsoft Windows NT

Microsoft  Windows  NT(new technology) is a 32 bit multi-user,  timesharing  operating  system  developed  by Microsoft.   It was designed  to have  UNIX-like  features  so that  it can be used  for powerful  workstations,   networks,  and  database  servers.  Like UNIX, Linux,   Windows  NT and  its subsequent  versions  has native  support  for networking   and  network  services. Such operating  systems  are classified  as Network  Operating  System  (NOS). Unlike  UNIX,  its native  interface  is a GUI.

LINUX

Linux  is a Unix-like computer operating system assembled under the model of free and open-source software development and distribution. Linux was originally developed for personal computers based on the Intel x86 architecture, but has since been ported to more platforms than any other operating system.

Operating System Techniques

Multiprogramming

It is thee process by which CPU works on two or more programs, simultaneously. Examples of operating system supporting multiprogramming are: OS/2, UNIX and Macintosh System 7.

Multiprocessing

It refers to the use of two or more CPU’s to perform a coordinated task simultaneously. For example, MVS, VMS and Windows NT.

Multitasking

It refers to the ability of an operating system to execute two or more tasks concurrently. In multitasking environment, the user open new applications without closing the previous ones and the information can be easily moved among a number of applications.

Multithreading

Threads are popular way to improve application performance. In traditional  operating  systems,  the basic unit of CPU utilization  is a process.   Each  process  has its own program  counter,  its own register  states,  its own stack, and its  own  address   space  (memory   area  allocated   to  it).    On  the  other  hand,  in  operating   systems,   with  threads facility,  the basic  unit of CPU utilization  is a  thread.   In these  operating  systems,  a process  consists  of an address counter,  its own register  states,  and its own  stack.