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  1. 1. Operating System (OS) • An operating system (OS) is the program that, after being initially loaded into the computer by a boot program, manages all the other programs in a computer. • The other programs are called applications or application programs. • The application programs make use of the operating system by making requests for services through a defined application program interface (API). • In addition, users can interact directly with the operating system through a user interface such as a command line or a graphical user interface (GUI).
  2. 2. Various services for applications • In a multitasking operating system where multiple programs can be running at the same time, the operating system determines which applications should run in what order and how much time should be allowed for each application before giving another application a turn. • It manages the sharing of internal memory among multiple applications. • It handles input and output to and from attached hardware devices, such as hard disks, printers, and dial-up ports.
  3. 3. Various services for applications • It sends messages to each application or interactive user (or to a system operator) about the status of operation and any errors that may have occurred. • It can offload the management of what are called batch jobs (for example, printing) so that the initiating application is freed from this work. • On computers that can provide parallel processing, an operating system can manage how to divide the program so that it runs on more than one processor at a time.
  4. 4. Classification of Operating systems • Multi-user: Allows two or more users to run programs at the same time. Some operating systems permit hundreds or even thousands of concurrent users. • Multiprocessing: Supports running a program on more than one CPU. • Multitasking : Allows more than one program to run concurrently. • Multithreading : Allows different parts of a single program to run concurrently. • Real time: Responds to input instantly. General-purpose operating systems, such as DOSand UNIX, are not real-time.
  5. 5. Most Popular Desktop Operating Systems • The three most popular types of operating systems for personal and business computing include Linux, Windows and Mac. • Windows • Microsoft Windows is a family of operating systems for personal and business computers. Windows dominates the personal computer world, offering a graphical user interface (GUI), virtual memory management, multitasking, and support for many peripheral devices.
  6. 6. Most Popular Desktop Operating Systems • Mac: • Mac OS is the official name of the Apple Macintosh operating system. Mac OS features a graphical user interface (GUI) that utilizes windows, icons, and all applications that run on a Macintosh computer have a similar user interface. • Linux: • Linux is a freely distributed open source operating system that runs on a number of hardware platforms. The Linux kernel was developed mainly by Linus Torvalds and it is based on Unix.
  7. 7. Batch operating system • The users of a batch operating system do not interact with the computer directly. Each user prepares his job on an off- line device like punch cards and submits it to the computer operator. To speed up processing, jobs with similar needs are batched together and run as a group. The programmers leave their programs with the operator and the operator then sorts the programs with similar requirements into batches. • The problems with Batch Systems are as follows − • Lack of interaction between the user and the job. • CPU is often idle, because the speed of the mechanical I/O devices is slower than the CPU. • Difficult to provide the desired priority.
  8. 8. Time-sharing operating systems • Time-sharing is a technique which enables many people, located at various terminals, to use a particular computer system at the same time. Time-sharing or multitasking is a logical extension of multiprogramming. Processor's time which is shared among multiple users simultaneously is termed as time-sharing. • The main difference between Multiprogrammed Batch Systems and Time-Sharing Systems is that in case of Multiprogrammed batch systems, the objective is to maximize processor use, whereas in Time-Sharing Systems, the objective is to minimize response time.
  9. 9. Time-sharing operating systems • Advantages of Timesharing operating systems are as follows − • Provides the advantage of quick response. • Avoids duplication of software. • Reduces CPU idle time. • Disadvantages of Time-sharing operating systems are as follows − • Problem of reliability. • Question of security and integrity of user programs and data. • Problem of data communication.
  10. 10. Distributed operating System • Distributed systems use multiple central processors to serve multiple real- time applications and multiple users. Data processing jobs are distributed among the processors accordingly. • The processors communicate with one another through various communication lines (such as high-speed buses or telephone lines). The advantages of distributed systems are as follows − • With resource sharing facility, a user at one site may be able to use the resources available at another. • Speedup the exchange of data with one another via electronic mail. • If one site fails in a distributed system, the remaining sites can potentially continue operating. • Better service to the customers. • Reduction of the load on the host computer. • Reduction of delays in data processing.
  11. 11. Network operating System • A Network Operating System runs on a server and provides the server the capability to manage data, users, groups, security, applications, and other networking functions. The primary purpose of the network operating system is to allow shared file and printer access among multiple computers in a network, typically a local area network (LAN), a private network or to other networks. • Examples of network operating systems include Microsoft Windows Server 2003, Microsoft Windows Server 2008, UNIX, Linux, Mac OS X, Novell NetWare, and BSD.
  12. 12. Network operating System • The advantages of network operating systems are as follows − • Centralized servers are highly stable. • Security is server managed. • Upgrades to new technologies and hardware can be easily integrated into the system. • Remote access to servers is possible from different locations and types of systems. • The disadvantages of network operating systems are as follows − • High cost of buying and running a server. • Dependency on a central location for most operations. • Regular maintenance and updates are required.
  13. 13. Real Time operating System • A real-time system is defined as a data processing system in which the time interval required to process and respond to inputs is so small that it controls the environment. The time taken by the system to respond to an input and display of required updated information is termed as the response time. So in this method, the response time is very less as compared to online processing. • Real-time systems are used when there are rigid time requirements on the operation of a processor or the flow of data and real-time systems can be used as a control device in a dedicated application. A real-time operating system must have well-defined, fixed time constraints, otherwise the system will fail. For example, Scientific experiments, medical imaging systems, industrial control systems, weapon systems, robots, air traffic control systems, etc.
  14. 14. Real Time operating System • There are two types of real-time operating systems. • Hard real-time systems • Hard real-time systems guarantee that critical tasks complete on time. In hard real-time systems, secondary storage is limited or missing and the data is stored in ROM. In these systems, virtual memory is almost never found. • Soft real-time systems • Soft real-time systems are less restrictive. A critical real- time task gets priority over other tasks and retains the priority until it completes. Soft real-time systems have limited utility than hard real-time systems. For example, multimedia, virtual reality, Advanced Scientific Projects like undersea exploration and planetary rovers, etc.
  15. 15. Embedded operating system • Embedded operating system are designed to be used in embedded computer system. • They are designed to operate on small machines like PDAs with less autonomy. • They are able to operate with a limited number of resources. They are very compact and extremely efficient by design. • Windows CE and Minix 3 are some examples of embedded operating systems.
  16. 16. Embedded operating system • The hardware running an embedded operating system can be very limited in resources such as RAM and ROM, therefore embedded design of these operating systems may have a narrow scope tailored to a specific application in order to achieve desired operation under these constraints. • In order to take better advantage of the processing power of the CPU, software developers may write critical code directly in assembly.
  17. 17. Library Operating System • A library operating system is one in which the services that a typical operating system provides, such as networking, are provided in the form of libraries and composed with the application and configuration code to construct a unikernel: a specialized, single address space, machine image that can be deployed to cloud or embedded environments.