The answer is Operating System. Operating system is nothing, it’s only a program that, when executed it controls the operations of computer. In Zeros generation and First generation of computers there was no operating system in computers. The Third generation computers had Operating system with some major advantages like Multiprogramming, Time-Sharing, Spooling etching Fourth generation there were so many operating systems developed like MS-DOS, UNIX, Windows NT etc.Today's the most recent client version of Windows version is Windows 7 and the most recent server version is Windows 2008 and the most recent mobile version is Windows phone 7.
Operating system is software of programs normally supplied along with the hardware for the effective and easy use of machine. It simply provides the environment within which other programs can do useful work. The two benefits which enhance its utility:
1) Security-Provision of security of information to users.
2) Duplicity-Elimination of duplicate efforts by hundreds of programmers in developing complicated routines.
Block diagram of Operating system:
The operating system controls the hardware and coordinates its use among the various application programs for the various users. The CPU, the Memory and the input/output device provides the basic computing resources for the system. The application programs such as word processor, spreadsheet, compilers and web browsers define the ways in which these resources are used to solve users computing problems.
We next explore operating systems from two viewpoints: that of user and that of system. The CPU, at a moment, can execute only one instruction .If this instruction is from the application program, the machine is said to be in the 'User mode’. If it is executing any operating system instruction, the machine is said to be in the 'System mode'.
User View-The user's view of the computer varies according to the interface being used. The System designed for one user to monopolize its resources is designed mostly for ease of use. Users sit at workstations connected to networks of other workstations and servers. Users share their resources. Therefore the operating system compromise between individual usability and resource utilization.
System View-In this context, we can view an operating system as a resource allocator. The operating system acts as a manger of resources like CPU time, memory space, file storage space, I/O devices. Operating system also view as a control program.A control program manages the execution of user programs to prevent errors and improper use of the computer.
Different Services of Operating System: The type of services that an operating system provides for reading and writing records. The three services are as follows:
1) Information Management
2) Process Management
3) Memory Management
1) Information Management: It refers to a set of services used for storing, retrieving, modifying and removing the information on various devices. Maintaining and enforcing the access controls to ensure that only right people have access information and driving various services, all this is managed by these system services. These services all normally provided by a single user operating system and as well as multiuser operating system.
2) Process Management: In multiuser operating system, a number of users located at different terminals run the same or different programs. At a given time, it can execute only one instructions belonging to any one all of these programs competing for the CPU.The function of operating system in this regard is to keep track of all competing processes, schedule them, dispatch them one after other, but while doing so, try to give each user an impression that he has full control of CPU.
3) Memory Management: These services provided under memory management are directed to keeping track of memory and allocating/deallocating it to various processes. The operating system keeps a list of memory locations.
One set of operating system services provides functions that are helpful to the user.
1) User interface -All operating systems have a user interface. The interface can take several forms. One is batch interface, in which commands and directives to control those commands are entered into files and those files are executed. Another is GUI (Graphical User Interface) is used. The Third one is Trace Command-line interface which uses text command.
2) Program Execution-The system must be able to load and run the program.
3) I/O operations: A running program may require I/O, which may involve file or an I/O device. A user cannot control I/O devices directly. Therefore, the operating system must provide a means to do.
4) File System Manipulation: Operating system provides a variety of file systems. Programs need to read and write files and directories. They also need to create them by name, search for a given file and list file information. These all services are provided by operating system n file systems.
5) Communication: Communications may be implemented by shared memory or message passing, in which packets of information are moved between processes by the operating system.
6) Error detection: Operating system also controls the error occurs in CPU and memory hardware. Debugging facilities can greatly enhance the user’s and programmer's abilities to use the system efficiently.
7) Resource allocation: Different types of resources allocation managed by operating system. Resources may be I/O devices, memory space, CPU cycles etc.
8) Accounting: Operating system also tracks which user use how much and what kinds of computer resources. This record keeping may be used for accounting.
9) Protection and Security: Protection involves ensuring that all access to system resources is controlled. Operating system must protect and secure the information.
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