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    Types of Operating System


    Some of the widely used operating systems are as follows

    Batch Operating System

    In this OS the user did not interact directly with the computer systems. The suer prepared a job using off-line device like punch cards, and submitted it to the computer operator. There is an operator which takes similar jobs having same requirement and group them into batches. It is the responsibility of operator to sort the jobs with similar needs. The output from each job would be sent back to the appropriate programmer. In this execution environment, the CPU is often idle, because the speeds of the mechanical I/O devices are intrinsically slower than are those of electronic device.

    "The operating system is termed as "batch operating" because the input data (job) are collected into batches or sets of records with similar needs and each batch is processed as a unit (group). The output is another batch that can be reused for computation." 

    Batch Processing SystemAdvantages 

    • Batch processing takes much of the work of the operator to the computer.
    • Increased performance as a new job gets started as soon as the previous job finished without any manual intervention. 

    Disadvantages

    • Difficult to debut program
    • A job could enter an infinite loop
    • The computer operators should be well known with batch systems
    • The other jobs will have to wait for an unknown time if any job fails 

    Multi Programmed Operating System

    In multiprogramming system, the operating system keeps several jobs in memory simultaneously. When one program is waiting for I/O transfer, there is another program ready to utilize the CPU. So, it is possible for several jobs to share the time of the CPU. In multiprogramming the execution of jobs is not defined at the same instance of time. To overcome the problem of utilization of CPU and main memory, the multiprogramming was introduced.

    Multi Programmed OSA simple process of multiprogramming is shown in the above figure. As given in fig. at the particular situation, job' A' is not utilizing the CPU time because it is busy in I/O operation. Hince the CPU becomes busy to execute the job 'B'. 

    Another jobs C, D, E, F are waiting for the CPU time for getting its execution time. So in this state the CPU will never be idle and utilizes maximum of its time.

    Time Sharing / Multi tasking Operating System

    Each task is given some time to execute, so that all the tasks work smoothly. Each user gets time of CPU as they use single system. These systems are also known as Multitasking Systems. The task can be from single user or from different users also. After the interval is over OS switches over to next task.

    Multi Tasking OSA time-shared operating system uses CPU scheduling and multiprogramming to provide each user with a small portion of a time-shared computer. Each user has at least one separate program in memory. 

    Advantage 

    • Provide advantage of quick response. 
    • Reduces CPU idle time

    Disadvantage

    • Reliability problem
    • Data communication problem

    Real time operating system

    These types of OSs serve the real-time systems. The time interval required to process and respond to inputs is very small. This time interval is called response time.

    "Real time system is defining as a data processing system in which each task has a deadline to complete. Real Time Operating system adheres to this deadline as missing a deadline can cause affects ranging from undesired to catastrophic. A real time system has well-defined, fixed time constraints."

    Two types of Real-Time Operating System which are as follows

    1. Hard Real-Time Systems

    These OSs are meant for the applications where time constraints are very strict and even the shortest possible delay is not acceptable. These systems are built for saving life like automatic parachutes or air bags which are required to be readily available in case of any accident. Virtual memory is almost never found in these systems.

    2. Soft Real-Time Systems

     

    In this type of OSs, missing a deadline is acceptable or time-constraint is less strict.

    Network Operating System

    Network operating system is client server architecture model. Some tasks of a Network Operating System are similar to those of an OS for individual computers, such as memory management and hardware control. 

    These systems run on a server and provide the capability to manage data, users, groups, security, applications, and other networking functions. These types of operating systems allow shared access of files, printers, security, applications, and other networking functions over a small private network.

    " A network operating system, or NOS, is system software that is designed primarily to controls the various devices like printer, disk drives on a computer network and how they communicate with each other." 

    Advantage

    • Highly stable centralized servers
    • Security concerns are handled through servers
    • Server access is possible remotely from different locations and types of systems

    Disadvantages 

    • Servers are costly 
    • User has to depend on central location for most operations

    Example: Artisoft's LANtastic, Novell's NetWare, Microsoft's LAN Manager, Windows NT, Open VMS etc.

    Distributed Operating System

    A distributed operating system is an extension of the network operating system that supports higher levels of communication and integration of the machines on the network. 

    A network, in the simplest term, is a communication path between two or more systems. Distributed system depends on networking for their functionality. 

    Bu being able to communicate, distributed systems are able to share computational tasks, and provide a reach set of features to users. 

    These systems are referred as loosely coupled systems where each processor has its own local memory and processors communicate with one another through various communication lines, such as high spee buses or telephone lines. Loosely coupled system, mean that such computer possess no hardware connections at the CPU memory bus level, but are connected by external interfaces that run under the control of software. 

    Advantage

    • Failure of one will not affect the other network communication, as all systems are independent from each other
    • Load on host computer reduces
    • Delay in data processing reduces

    Disadvantages

    • Failure of the main network will stop the entire communication
    • These types of systems are not readily available as they are very expensive. Not only that the underlying software is highly complex and not understood well yet

    Multiprocessor Operating System

    "Multiprocessor system also known as parallel systems or tightly coupled systems have more than one processor in close communication, sharing the computer bus, the clock, and sometimes memory and peripheral devices."

    Types of Multiprocessor system

    Shared Memory Multiprocessor system: A natural extension of a single processor system in which all the processor can access a common memory.

    Distributed memory multicomputer system: Multiple interconnected computers where each computer has its own memory.


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