Operating System

                          

 OPERATING SYSTEM

Operating system (often referred to as OS) is an integrated set of programs that controls the resources (CPU, memory, I/O devices, etc.) of a computer system and provides its users with an interface or virtual machine that is easier to use than the bare machine. According to this definition, the two
primary objectives of an operating system are:

   (1.)  Make a computer system easier to use:

  A computer system consists of one or more processors, main memory, and many types of I/O devices such as disks, tapes, terminals, network interfaces, etc. Writing program for using these hardware resources correctly and efficiently is an extremely difficult job, requiring in-depth knowledge of functioning of these resources. Hence, to make computer systems useable by a large number of users, it become clear several years ago that computer systems need some mechanism to shield programmers and other users from the complexity of hardware resources. Researchers gradually evolved a solution to handle this problem by putting a layer of software on top of the bare hardware. This layer of software manages all hardware resources of the system, and presents the users with an interface or virtual machine that is easier, safer, and efficient to program and use. It is called the operating system.

Hence an operating system hides details of hardware resources from programmers and other users. It provides a high-level interface to low-level hardware resources, making it easier for programmers and other users to use a computer system.

 
(2.)  Manage the resources of a computer system:

An operating system manages all the resources of a computer system. This involves performing such tasks as keeping track of who is using what resources, granting resources requests, accounting for resources usage, and mediating conflicting requests from different programmers and users. Efficient and fair sharing of system resources among users and/or programs is a key goal of all operating systems.

    MAIN FUNCTIONS OF AN OPERATING SYSTEM

Most operating systems perform the functions given below. A separate module of operating system software performs each of these functions:

   (1.)  Process Management:

 A process is a program in execution. During execution, a process needs certain resources such as CPU time, memory space, files, and I/O devices. At a particular instance of time, a computer system normally consists of a collection of processes. Process management module takes care of creation and deletion of processes, scheduling of system resources to different processes requesting them, and providing mechanisms for synchronization and communication among processes.

   (2.)  Memory Management:

To execute a program, it must be loaded in main memory (at least partially), together with the data it accesses. To improve CPU utilization and to provide better response time to its users, a computer system normally keeps several programs in main memory. Memory management module takes care of system of allocation and de-allocation of memory space to programs in need of this resources.

   (3.)  File Management:

All computer systems store, retrieve, and share information. Normally, a computer stores such information in units called files. Processes read from files and create new files for storing newly generated information. File management module takes care of file-related activities such as organization, storage, retrieval, naming sharing, and protection of files.

   (4.)  Device Management:

Normally, a computer system consists of several I/O devices such as terminal, printer, disk, and tape. The device management module of an operating system controls all I/O devices. It keeps track of I/O requests from processes issues commands to I/O devices, and ensure correct data transmission to/form an I/O device. It also provides a simple and easy to use interface between the devices and rest of the system.

   (5.)  Security:

Computer systems often store large amount of information, some of which are highly sensitive and valuable to their users. Users can trust a computer system and rely on it only if its various resources and information stored in it are protected against destruction and unauthorized access. Security module protects the resources and information of computer system against destruction and unauthorized access. It also ensure that when the system executes several disjoint processes simultaneously, one process does not interfere with others or with the operating system itself.

    (6.)  Command Interpretation:

For using various system resources, a user communicates with the operating system via a set of commands provided by it. The operating system also provides a simple language, known as command language (CL) or job control language (JCL); using which a user can put several commands together from the command set to describe the resource requirements of a job. Command interpretation module interprets user commands and directs system resources to process the commands. With this mode of interaction with a system, users are not much concerned about hardware details of the system.

An operating system also performs few other functions such as accounting of system resource usage by all users (or processes), maintenance of log of system usage by all users, and maintenance of internal time clock.