OS Notes Done - Important Topics PDF

Preview

Summary

What is GUIA GUI (graphical user interface) is a system of interactive visual components for computer software. A GUI displays objects that convey information, and represent actions that can be taken by the user. The objects change color, size, or visibility when the user interacts with them. GUI ob...

Description

What is GUI

What is Operating System?

A GUI (graphical user interface) is a system of interactive visual components for computer software. A GUI displays objects that convey information, and represent actions that can be taken by the user. The objects change color, size, or visibility when the user interacts with them. GUI objects include icons, cursors, and buttons. These graphical elements are sometimes enhanced with sounds, or visual effects like transparency and drop shadows. A GUI is considered to be more user-friendly than a text-based command-line interface, such as MS-DOS, or the shell of Unix-like operating systems.

An Operating System (OS) is an interface between a computer user and computer hardware. An operating system is a software which performs all the basic tasks like file management, memory management, process management, handling input and output, and controlling peripheral devices such as disk drives and printers. Some popular Operating Systems include Linux Operating System, Windows Operating System, VMS, OS/400, AIX, z/OS, etc. An operating system is a program that acts as an interface between the user and the computer hardware and controls the execution of all kinds of programs OS is a collection of software which manage the resources of computer system like memory processor, File System and input output devices. O/S keep track of the status of each resource and decides who will have control over computer resources for how long and when There are two way to interact with OS 1 System call 2 Command (O/S Command)

Feature Of GUI 1.It provides various Secondary user input device like painting driver mouse etc. 2.It provide point and short functionality on the screen in the form of menus. 3.It uses icons that rep files directories and other application 4.It provides daily boxes button slides checkbox and many other graphical component

The3D GUI The desktop metaphor GUI is 2% D. It is 2D because its visual elements are two dimensional: they lie in the xy plane, are defined in 2D coordinates, are flat and contain only planar regions (areas). It is 2% D because where visual elements overlap, they obscure each other according to their priority. In a 3D GUI the visual elements are genuinely three-dimensional: they are situated in xyz space, are defined in terms of 3D coordinates. The design considerations for a 3D GUI appear more complex than for a 2% D GUI. To begin with, the issues of metaphor and elements arise afresh. The desktop metaphor with its windows, icons, menus and pointing device elements is firmly established for 2!4D GUIs. Tn contrast no clearly defined metaphor and set of elements for 3D GUIs are manifest -yet. 3D GUIs offer considerably more scope for metaphors than 2%D GUIs; the desktop metaphor into a 3D environment, including the obvious extension other desktop metaphor into a 3D office metaphor. On the other hand, much more abstract metaphors are possible, such as one based "starmaps" where objects are simply placed somewhere in "cyberspace". Likewise, the elements of a 3D GUI may resemble, or differ substantially from, the elements of the 2% D GUI. The development environment for most GUIS consists of four major components: 1.Windowing systems allow programs to display multiple applications at the same time. Fundamentals & Windowing systems include programming tools for building movable and resizable Networking windows, menus, dialog boxes and other items on the display. Macintosh. Others use common windowing systems such as X-window or simple X. 2.An imaging model defines how fonts and graphics are created on the screen. This component of the system environment has taken on increasing sophistication as applications incorporate complex curves, color, shading and dimension. Some GUIs support more than one imaging model. 3.The API is a set of programming language functions that allow the programmer to specify how the actual application will control the menus, scroll bars and icons that appear on the screen. Like windowing models, APIs align with particular GUIs.

X Window The name X, as well as part of the initial design, was derived from an earlier window system called W developed at Standford University. Currently, the X Window system is supported by an X Consortium of primarily UNIX-based hardware and software vendors as a standard base for user interfaces across most UNIX product lines. the components of UNIX GUIs based on X Windows. The X Window system does not define any particular style of interface but rather provides a mechanism for supporting many styles. X is also network-based. In contrast with PM, the X architecture is based on the premise that an application can run one computer, while the graphical presentation of the application's output and responses from the user can occur on another computer. X does not provide user interface components such as buttons, menus, or dialog boxes. An interface supporting X can theoretically use any XWindow display. The application program sends calls to the X-Window Library, which packages the requests as X packets and sends calls to the X-Window server. The server decodes the X packets and displays them on the screen. Exactly how the packets will be displayed (i.e. will look) on a workstation depends on the set of pre-designed window elements called widgets that are unique to the particular workstation in the system environment. The ultimate look on one workstation may differ substantially from that on another, but the response to a user's action on these different-looking interfaces will be the same. Several hybrids of X exist.

Memory Management Memory management refers to management of Primary Memory or Main Memory. Main memory is a large array of words or bytes where each word or byte has its own address. Main memory provides a fast storage that can be accessed directly by the CPU. For a program to be executed, it must in the main memory. An Operating System does the following activities for memory management– Keeps tracks of primary memory, i.e., what part of it are in use by whom, what part are not in use. In multiprogramming, the OS decides which process will get memory when and how much. Allocates the memory when a process requests it to do so. De-allocates the memory when a process no longer needs it or has been terminated.

Processor Management In multiprogramming environment, the OS decides which process gets the processor when and for how much time. This function is called process scheduling. An Operating System does the following activities for processor management − Keeps tracks of processor and status of process. The program responsible for this task is known as traffic controller. Allocates the processor (CPU) to a process. De-allocates processor when a process is no longer required.

Device Management An Operating System manages device communication via their respective drivers. It does the following activities for device management − Keeps tracks of all devices. Program responsible for this task is known as the I/O controller. Decides which process gets the device when and for how much time. Allocates the device in the efficient way. De-allocates devices.

File Management A file system is normally organized into directories for easy navigation and usage. These directories may contain files and other directions. An Operating System does the following activities for file management − Keeps track of information, location, uses, status etc. The collective facilities are often known as file system. Decides who gets the resources. Allocates the resources. De-allocates the resources.

Multithreading Multithreading is a technique in which a process executing an application is divided into threads that can run concurrently. We can make the following distinction: Threads: A dispatchable unit of work. It includes a processor context (which includes the program counter and stack pointer) and its owl1 data area for a stack (to enable subroutine branching). A thread executes sequentially and is interruptible so that the processor can turn to another thread. Process: A collection of one or more threads and associated system resources (such as memory containing code and data, open files, and devices). This corresponds closely to the concept of a program in execution. By breaking a single application into multiple threads, the programmer has great control over the modularity of the application and the timing of application related events. Multithreading is useful for applications that perform a number of essentially independent tasks that do not need to be serialized. multiple threads running within the same process, switching back and forth among threads involves less processor overhead than a major process switch between different processes. Threads are also useful for structuring processes that are part of the OS kernel

Type of OS Multiprocessor Operating Systems A typical multiprocessor system consists of a set of processors that share a set of physical memory blocks over an interconnection network. Thus, a multiprocessor system is a tightly coupled system where processors share an address space. A multiprocessor operating system controls and manages the hardware and software resources such that users view the entire systems as a powerful uniprocessor system; a user is not aware of the presence of multiple processors and the interconnection network. The basic issues in the design of a multiprocessor operating system are the same as in a traditional operating system. However, the issues of process synchronisation, task scheduling, memory management, and protection and security become more complex because the main memory is shared by many physical processors.

Distributed Operating System Distributed operating systems are operating systems for a network of autonomous computers connected by a communication network. A distributed operating system controls and manages the hardware and software resources of a distributed system such that its users view the entire system as a powerful monolithic computer system. When a program is executed in a distributed system, the user is not aware of where the program is executed or of the location of the resources accessed. The basic issues in the design of a distributed operating system are the same as in a traditional operating system, viz., process synchronization, deadlocks, scheduling, file systems, interposes communication, memory and buffer management, failure recovery, etc. However, several idiosyncrasies of a distributed system, namely, the lack of both shared memory and a physical global clock, and unpredictable communication delays make the design of distributed operating systems much more difficult. Network operating systems focus on the use of remote services and resources existing on a network of computer systems. Distributed operating systems focus on effective utilization of resources in distributed computing environments. Distributed systems provide many advantages concerning cost-effectiveness of both computations and resources. The primary advantages are: Resource sharing Reliability Communication Incremental growth

Network Operating A network operating system is a collection of software and associated protocols that allows a set of autonomous computers, which are interconnected by a computer network, to be used together in a convenient and cost-effective manner. In a network operating system, the users are aware of the existence of multiple computers and can log in to remote machines and copy files from one machine to another machine. Some of typical characteristics of network operating systems which make it different from a distributed operating system (discussed in the next section) are the followings: Each computer has its own private operating system instead of running part of a global system wide operating system. Each user normally works on his/her own system: using a different system requires some kind of remote login, instead of having the operating system dynamically allocate processes to CPUs. Users are typically aware of where each of their files are kept and must move file from one system to another with explicit file transfer commands instead of having file placement managed by the operating system.

Distributed Operating Distributed operating systems are operating systems for a network of autonomous computers connected by a communication network. A distributed operating system controls and manages the hardware and software resources of a distributed system such that its users view the entire system as a powerful monolithic computer system. When a program is executed in a distributed system, the user is not aware of where the program is executed or of the location of the resources accessed. Distributed systems provide many advantages concerning cost-effectiveness of both computations and resources. The primary advantages are: Resource sharing Reliability Communication Incremental growth

Virtual Machine It is a concept which creates the illusion of a real machine. It is created by virtual machine operating system that makes a single real machine appear to be several real machines. This type of situation is analogous to the communication line of Telephone Company, which enables separate and isolated conversations over the same wire(s). Virtual Machine abstracts the hardware of our personal computer such as CPU, disk drives, memory, NIC (Network Interface Card) etc., into many different execution environments as per our requirements, hence giving us a feel that each execution environment is a single computer. For example, VirtualBox. Advantages: There are no protection problems because each virtual machine is completely isolated from all other virtual machines. Virtual machine can provide an instruction set architecture that differs from real computers. Easy maintenance, availability and convenient recovery. Disadvantages: When multiple virtual machines are simultaneously running on a host computer, one virtual machine can be affected by other running virtual machines, depending on the workload. Virtual machines are not as efficient as a real one when accessing the hardware.

What is computer network? What is the need of different network topologies? Explain structure of Bus topology and star topology A computer network is a group of computers that use a set of common communication protocols over digital interconnections for the purpose of sharing resources located on or provided by the network nodes. The interconnections between nodes are formed from a broad spectrum of telecommunication network technologies, based on physically wired, optical, and wireless radio-frequency methods that may be arranged in a variety of network topologies. The topology is the geometric arrangement (either physically or logically) other linking devices (usually called nodes) and the links, connecting the individual computers or nodes together. Five basic topologies: 1) Bus topology 2) Ring topology 3) Star topology 4) Mesh topology 5) Combined topologies.

The BUS Topology 1n the bus topology there is a single bus that carries all the data to the entire network. A bus is a single continuous communication cable to which all the computers are connected. A cable or bus runs throughout the office to which all the workstations are connected. The bus topology is also known as linear bus.

Ring topology A ring topology is a network configuration where device connections create a circular data path. Each networked device is connected to two others, like points on a circle. Together, devices in a ring topology are referred to as a ring network. In a ring network, packets of data travel from one device to the next until they reach their destination. Most ring topologies allow packets to travel only in one direction, called a unidirectional ring network. Others permit data to move in either direction, called bidirectional.

The Star Topology In the star topology all the stations are connected to a central computer or hub creating a star configuration. The devices are not directly linked to each other Messages pass from the nodes to the hub, where they are processed or passed along to another node. The hub controls the traffic on the network. If the hub fails, the entire network becomes inoperative, but if a node fails it does not affect the rest of the traffic on the network

Mesh Topology Mesh Topology?. In the Digital era, apart from computers and printers, Machines, Equipment, Home appliances, and Personal Gadgets are networked with each other as well as connected to the internet. The network plays an important role by connecting people, machines and any devices to share information and do transactions. The selection of the right topology of the network depends on business objectives, enduser requirements and the IT policy of any organization. It plays a crucial role in the performance of the network and controlling the operating cost. Topology describes the way nodes in the network are connected physically and logically with each other and with servers.

OSI Model OSI stands for Open System Interconnection is a reference model that describes how information from a software application in one computer moves through a physical medium to the software application in another computer. OSI model divides the whole task into seven smaller and manageable tasks. Each layer is assigned a particular task. Each layer is self-contained, so that task assigned to each layer can be performed independently.

The OSI model is divided into two layers: upper layers and lower layers. The upper layer of the OSI model mainly deals with the application related issues, and they are implemented only in the software. The application layer is closest to the end user. Both the end user and the application layer interacts with the software applications. An upper layer refers to the layer just above another layer. The lower layer of the OSI model deals with the data transport issues. The data link layer and the physical layer is implemented in hardware and software. The physical layer is the lowest layer of the OSI model and is closest to the physical medium. The physical layer is mainly responsible for placing the information on the physical medium.

Computer Network Types A computer network is a group of computers linked to each other that enables the computer to communicate with another computer and share their resources, data, and applications. A computer network can be categorized by their size. A computer network is mainly of four types:

LAN(Local Area Network) Local Area Network is a group of computers connected to each other in a small area such as building, office. LAN is used for connecting two or more personal computers through a communication medium such as twisted pair, coaxial cable, etc. It is less costly as it is built with inexpensive hardware such as hubs, network adapters, and ethernet cables. The data is transferred at an extremely faster rate in Local Area Network. Local Area Network provides higher security. PAN(Personal Area Network) Personal Area Network is a network arranged within an individual person, typically within a range of 10 meters. Personal Area Network is used for connecting the computer devices of personal use is known as Personal Area Network. Thomas Zimmerman was the first research scientist to bring the idea of the Personal Area Network. Personal Area Network covers an area of 30 feet. Personal computer devices that are used to develop the personal area network are the laptop, mobile phones, media player and play stations

Wireless Personal Area Network: Wireless Personal Area Network is developed by simply using wireless technologies such as WiFi, Bluetooth. It is a low range network. Wired Personal Area Network: Wired Personal Area Network is created by using the USB.

MAN(Metropolitan Area Network) A metropolitan area network is a network that covers a larger geographic area by interconnecting a different LAN to form a larger network. Government agencies use MAN to connect to the citizens and private industries. In MAN, vario...