1. Simple Batch System

 2. Multiprogramming Batch System

 3. Multiprocessor System

 4. Distributed Operating System

 5. Realtime Operating System

  >> SIMPLE BATCH SYSTEMS

  In this type of system, there is no direct interaction between user and the computer.

 The user has to submit a job (written on cards or tape) to a computer operator.

 Then computer operator places a batch of several jobs on an input device.

 Jobs are batched together by type of languages and requirement.

 Then a special program, the monitor, manages the execution of each program in the batch.

 The monitor is always in the main memory and available for execution.

 Following are some disadvantages of this type of system :

  Zero interaction between user and computer.

 No mechanism to prioritize processes.

  >> MULTIPROGRAMMING BATCH SYSTEMS

  In this the operating system, picks and begins to execute one job from memory.

 Once this job needs an I/O operation operating system switches to another job (CPU and OS always busy).

 Jobs in the memory are always less than the number of jobs on disk(Job Pool).

 If several jobs are ready to run at the same time, then system chooses which one to run (CPU Scheduling).

 In Non-multiprogrammed system, there are moments when CPU sits idle and does not do any work.

 In Multiprogramming system, CPU will never be idle and keeps on processing.

 Time-Sharing Systems are very similar to Multiprogramming batch systems.

 In fact time sharing systems are an extension of multiprogramming systems.

 In time sharing systems the prime focus is on minimizing the response time, while in multiprogramming the prime focus is to maximize the CPU usage.

  >> MULTIPROCESSOR SYSTEMS

  A multiprocessor system consists of several processors that share a common physical memory.

 Multiprocessor system provides higher computing power and speed. In multiprocessor system all processors operate under single operating system.

 Multiplicity of the processors and how they do act together are transparent to the others.

  Following are some advantages of this type of system.

  Enhanced performance

 Execution of several tasks by different processors concurrently, increases the system's throughput without speeding up the execution of a single task.

 If possible, system divides task into many subtasks and then these subtasks can be executed in parallel in different processors. Thereby speeding up the execution of single tasks.

  >> DISTRIBUTED OPERATING SYSTEMS

  The motivation behind developing distributed operating systems is the availability of powerful and inexpensive microprocessors and advances in communication technology.

  These advancements in technology have made it possible to design and develop distributed systems comprising of many computers that are inter connected by communication networks.

 The main benefit of distributed systems is its low price/performance ratio.

  Following are some advantages of this type of system.

  As there are multiple systems involved, user at one site can utilize the resources of systems at other sites for resource-intensive tasks.

 Fast processing.

 Less load on the Host Machine.

  >> REAL-TIME OPERATING SYSTEM

  It is defined as an operating system known to give maximum time for each of the critical operations that it performs, like OS calls and interrupt handling.

  The Real-Time Operating system which guarantees the maximum time for critical operations and complete them on time are referred to as Hard Real-Time Operating Systems.

  While the real-time operating systems that can only guarantee a maximum of the time, i.e. the critical task will get priority over other tasks, but no assurity of completeing it in a defined time.

 These systems are referred to as Soft Real-Time Operating Systems.

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