Operating System

An Operating System is a system software, consisting of an integrated set of programs that controls computer resources (CPU, memory, I/O devices, etc) and provides common services for efficient execution of various application software with an interface or virtual machine that is more convenient to use.

Need for an Operating System

At the simplest level, an operating system does two things: (i) It manages the hardware and software resources of the system. In a desktop computer, these resources include such things as the processor, memory, disk space etc.

(ii) It provides a stable, consistent way for applications to deal with the hardware without having to know all the details of the hardware.

Functions of Operating System

The operating system controls and coordinates the use of hardware among various application programs for various users.

Various functions of operating system are:

  1. Resource utilization allocation
  2. Resource 3. Process control and management
  3. File management 5. Communication
  4. Information maintenance 7. Device management

User Interface User interface is that part of the operating system, which is visible to the user and has to be understood by the user. There are two types of user interfaces:(i) Character User Interface (CUI) It is a means of interacting with computer program, where the user issues commands to the program in the form of successive lines of text (command lines). It was used by DOS.(ii) Graphical User Interface (GUI) It is a program interface that takes advantage of the computer’s graphics capability to make the program easier to use. In this interface, the commands are given by selecting or clicking on the options, which can be identified with the small figures that appear with them.Types of Operating System There are different types of operating systems available, which require different types of hardware to run on.The operating systems are classified as:Single User Operating System Single user operating system is a type of operating system, which allows only one user at a time. Operating system for Personal Computer (PC) is single user operating system. They are designed to manage one task at a time. e.g. MS-DOS, WINDOWS 9X.

18Multi-User Operating System This operating system allows multiple users to access computer system .concurrently. It is used in computer networks that allow same data and applications to be accessed by multiple users at the same time.e.g. UNIX, LINUX, WINDOWS 2000/7Multi-Tasking Operating System In multi-tasking operating system, more than one processes can be executed concurrently. It also allows the user to switch between the running applications. e.g. LINUX, UNIX, WINDOWS 95. Batch Processing Operating System In batch processing operating system, a number of jobs are put together and executed as a group. This operating system is responsible for scheduling the jobs according to priority and the resource required.Multi-Programming Operating System In multi-programming operating system, more than one program reside in the main memory. When one job is unable to execute because of I/O operation, it switches to another program and allows that program to run.Time Sharing Operating System In time sharing, a small amount of time is allocated for the processing simultaneously e.g. Mac OS. The time sharing operating system allows multiple programs to simultaneously share the computer resources. Time sharing operating system provides scheduling to each process to berun on.Real Time Operating System (RTOS)The main objective of real time operating systems is their quick and predictable response to events than any other operating system. Real time operating systems are designed to respond to an event within a predetermined time. It must have preemptive kernels to execute a program. c.g. Lynx OS, HP-RT.There are two types of real time operating system: (i) Hard Real Time OS (ii) Soft Real Time Os Embedded Operating Systema embedded operating system refers to the operating system that is self contained in the device and resident in theRead Only Memory (ROM) e.g. WINDOWS CE, Minix-3, etc.

Distributed Operating SystemDistributed means data can be stored and processed on multiple locations. Distributed operating system use multiple central processor to serve multiple real-time applications.Mobile Operating SystemA mobile OS is an OS that operates on Smart Phones, Tablets and Digital Mobile devices. e.g. Android, Symbian etc.ProcessA process is simply defined as program under execution. Thus, the difference between process and program is that program is a passive entity whereas process is active entity.Process StateWhen a process executes, it changes its state. The state of process is defined as part of the current activity of the process. Each process may be in one of the following states.AdmittedInterruptExitNewReadyRunningTerminatedCPU allocated1/0 demandVO operation completionWaitingProcess StateNewThe process is being created.RunningInstructions are being executed.WaitingThe process is waiting for some event to occur (such as completion of I/O operation or reception of a signal).ReadyThe process is waiting to be assigned to a processor.TerminatedThe process has finished its execution. Each process is represented in operating system by a Process Control Block (PCB) also known as task central block.ובe

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