Operating System
An operating system is a program that controls the execution of application programs and acts as an interface between the user of a computer and the computer hardware. A more common definition is that the operating system is the one program running at programs.
An operating system is concerned with the allocation of resources and services, such as memory, processors, devices, and information. The operating system correspondingly includes programs to manage these resources, such as a traffic controller, a scheduler, a memory management module, I/O programs, and a file system.
Functions of Operating System:
Memory management: It manages both the primary and secondary memory such as RAM, ROM, hard disk, pen drive, etc. It checks and decides the allocations and deallocation of memory space to different processes.
Processor Management: It facilitates processor management, where it decides the order for the processes to access the processor as well as decides the processing time to be allocated for each process. Besides this, it monitors the status of processes, frees the processor when a process is executed then allocates it to a new process.
Run software applications: It offers the environment to run or use software applications developed to perform specific tasks, for example, Ms Word, Ms Excel, Photoshop, etc.
Provides user interface: It acts as an interface between the user and the hardware. It can be a GUI where you can see and click elements on the screen to perform various tasks. It enables you to communicate with the computer even without knowing the computer's language.
I/0 management: It manages the input output devices and makes the I/O process smooth and effective. For example, it receives the input provided by the user through an input device and stores it in the main memory. Then it directs the CPU to process this input and accordingly provides the output through an output device such as a monitor.
Time Management: It helps CPU in time management. The Kernel OS keeps checking the frequency of processes that requests CPU time. When two or more processes that are equally important compete for the CPU time, then the CPU time is sliced into segments and allocated to these processes in a round-robin fashion to prevent a single process from monopolizing (taking control) the CP.
Deadlock Prevention: Sometimes a resource that is supposed to be shared by two or more processes is held by one process due to which the resource cannot continue.This situation is known as deadlock The OS does not let this situation arise by carefully distributing the resources among the different processes.
Interrupt Handling: OS also responds to interrupts, which are signals generated by a program or a device to seek the attention of the CPU. The OS checks the priority of the interrupt, and if it is more important than the currently running process, it stops the execution of the current process and preserves this state of CPU then executes the requested process. Thereafter the CPU returns to the same state where it was stopped.
Interrupt can be of two type:
■ Hardware interrupt: Interrupting signals generated by hardware devices such as a keyboard, printer or chips on the system board is called hardware interrupts.For example, when we press a key on the keyboard or move the mouse, they trigger hardware interrupts which cause the processor to read the keystroke or mouse position.
■Software interrupt: Interrupting signals generated or caused by programs or software are called software interrupts. For example, if a program expects a variable to be a valid number, but the value is null, an interrupt may be generated to prevent the program from crashing.
Types of Operating System based on User Interface
User Interface
A User interface (UI) facilitates communication between an application and its user by acting as an intermediary between them. Each application including the operating system is provided with a specific UI for effective communication. The two basic function of a user interface of an application is to take the inputs from the user and to provide the output to the users. However, the types of inputs taken by the UI and the types of output provided by the UI may vary from one application to another. A user interface of any operating system can be classified into one of the following types:
1. Graphical user interface (GUI)
2. Command line user interface (CUI)
Graphical user interface (GUI)
The graphical user interface is a type of GUI that enables the users to interact with the operating system by means of point-and-click operations. GUI contains several icons. representing pictorial representation of the variables such as a file, directory, and device. The graphical icon provided in the UI can be manipulated by the users using a suitable pointing device such as a mouse, trackball, touch screen and light pen. The other input devices like keyboard can also be used to manipulate these graphical icons. GUIs are considered to be very user-friendly interface because each object is represented with a corresponding icon. Unlike the other UIs the users need not provide text command for executing tasks.
Command User/line Interface (CUI/CLI)
Command line interface is a type of UI that enables the users to interact with the operating system by issuing some specific commands. In order to perform a task in this interface, the user needs to type a command at the command line. When the user enters the key, the command line interpreter received a command. The software program that is responsible for receiving and processing the commands issued by the user. After processing the command are called command line interpreter, the command line interpreter displays the command prompt again along with the output of the previous command issued by the user. The disadvantages of the CLI is that the user.
Types of Operating System based on User Mode
The number of users that can use the computer resources at a time is called user mode.
There are two types of operating system:
1. Single User
● It allows one user at a time. All the resources of the system are availablebto the user. If another user needs access to the computer system, they must wait till the current user finishes what they are doing and leaves.Eg: MS-DOS
2. Multi User
● It allows two or more users to run programs at the same time. The multi-user OS shares computer resources among these users, allowing each a small slice of processor time. This concept is known as time sharing.Eg: Unix, Linux
Types of Operating System based on Processing
Batch Processing Operating System:
➢ The interaction between a user and the computer does not occur in this system.
The user is required to prepare jobs on punch cards in the form of batches and submit them to the computer operator. The computer operator sorts the jobs or programs and keeps similar programs or jobs in the same batch and run as a group to speed up processing. It is designed to execute one job at a time. Jobs are processed on a first-come, first-serve basis, i.e., in the order of their submission without any human intervention.
Multiprogramming Operating System
A multiprogramming operating system may run many programs on a single processor computer. If one program must wait for an input/output transfer in a multiprogramming operating system, the other programs are ready to use the CPU. As a result, various jobs may share CPU time.
Multi Tasking Operating System
It is a logical extension of a multiprogramming system that enables the execution of multiple programs simultaneously. In an operating system, multitasking allows a user to perform more than one computer task simultaneously. Multiple tasks are also known as processes that share similar processing resources like a CPU. Multitasking is similar to multiprogramming in that the CPU is assigned to a process for a specified period of time.
Multiprocessing Operating system
In operating systems, to improve the performance of more than one CPU can be used within one computer system called Multiprocessor operating system.Multiple CPUs are interconnected so that a job can be divided among them for faster execution. When a job finishes, results from all CPUs are collected and compiled to give the final output. Jobs needed to share main memory and they may also share other system resources among themselves.
Time Sharing Operating System:
As the name suggests, it enables multiple users located at different terminals to use a computer system and to share the processor's time simultaneously. In other words,each task gets time to get executed, and thus all tasks are executed smoothly.Each user gets the processor's time as they get while using a single system. The duration of time allocated to a task is called quantum or time slice; when this duration is over, OS starts the next task.
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