Different types of Operating System

1.    Batch Operating System

2.    Distributed System

3.    Multi-programmed system

4.    Time sharing

5.    Real Time

1. Batch System: -

                           In earlier days, the common input devices were card reader

and tape drives. The common output devices were line printers, tape drives and card punches. In these type of system user did not interact directly with computer system. Users prepare a job (which consists of program or data) and submit it to the computer operator. The job was usually in the form of punched cards at latest time (at the end of the day or end of the month). The user submits this information to the computer. The output computer consists of a result of program or data in print format. The major task of operating system was to transfer control automatically from one job to next job. The operating system is always resident in memory and it executes the job sequential. To speed up processing operators, fetched together jobs with similar needs and run them through the computer as a group. The operator would sort the programs into batches with similar requirements and submit it to the computer and it would run each batch. In this type of operating system the CPU is often ideal because the speed of mechanical input/output devices is slower than CPU.

2. Distributed System: -

                                      Network in its simplest terms, is a communication path between two systems. This type of system depends on networking or  

their functionality. To communicate with distributed system, it is used to share the information and it provides a rich set of features to users like accessing different resources available at another computer. Networks vary by protocols and distances between two computers (it is a set of rules which offers conversation between two computer systems = protocol) Ex. TCP/IP. IP is the most common network protocol. Most operating systems support TCP and IP including WINDOWS and UNIX. A network protocol simply needs an interface card, network adapter driver to manage it. Networks are divided on the base of the distance between the computers.

1.    LAN – Local area network exists within a room, a floor or a building.

2.    MAN– Metropolitan area network is a type of network, which exists within buildings of different cities.

3.    WAN– Wide area network exists between different countries. Ex. Internet - The media to carry network equally varied. The network media includes copper wires, co-axial cables, fiber optics and satellites.       

3. Multi Program Operating System: -

                                                         A single user cannot keep the CPU for Input/Output devises busy at time. Multiprogramming increases CPU utilization by organizing jobs so that CPU always executes one job. The operating system keeps similar jobs in memory simultaneously, is subset of the job, which are kept in the job pool. The number of jobs that can be kept simultaneously is usually much smaller than the number of jobs that can be in the job pool. The operating system picks & begins to execute one of the job in the memory when the job have to wait for some task such as the input/output operation it complete than it executes the job. In not multi-programming operating system CPU will sit ideal. In multi-programming system, the OS switches executes another job when that job needs to wait, the CPU is switched to another job and so on. The first job finishes waiting gets the CPU back as long as at least one job needs to execute in this type of environment. CPU never becomes deal. Multiprogramming is the first instance where the OS must take decisions for the users. This type of operating system is fairly sophisticated. If similar jobs are ready to be brought into memory and if there is not enough room for all then the system must decide among them. Making this decision is called decision scheduling. When the operating system selects the job from job pool, it loads that job into memory for execution. If similar jobs are ready to run, the system must decide among them. Making this decision is called CPU scheduling. 

Memory Management For Multi Program System 

4. Time Shared System: -

                                        Multi program, batch system provides an environment where the various system resources are utilized effectively but it does not provide user interaction with computer resource. Time shared (multi tasking) is a logical extension of multi programming. The CPU executes multiple jobs by switching among them but the switches occur so frequently that the user can interact with each program while it is running. This is a interactive with the user and it provides direct communication between the user and terminal. The user gives instruction to the operating system using keyboard or mouse and waits for immediate results. The response time should be short typically in the range of fraction or seconds. Time-shared operating system allows any user to share computer simultaneously. Since each action or command in this type of operating system tends to be short, only a little CPU time is needed for each user. As the system switches rapidly from one user to next, each user is given the impression that entire computer system is dedicated to his thoughts; it is being said among any user. Time sharing systems are difficult and expensive to build. They did not become common until 1970s. Most systems today are time-shared operating system. Multi programming and time-sharing are central themes of modern operating system.

5. Real Time Systems: -

                                    It is a special purpose operating system. It is used when rigid time requirement have been placed on the operation of a procedure or the flow of data. It is often used as a control device dedicated to the application. System that controls scientific experiments, medical imaging system, industrial control system and certain display system are real time systems. Some automobile engines, fuel injection system, home appliance controllers and weapons systems are also real time systems. A real time system has a well defined fixed time constraint in which processing must be done within that constraint otherwise the system will fail. A real time system functions correctly only if it returns the result within its time constraint. Contrast with time-sharing where it is desirable to respond quickly. A batch system, which may not have any time constraint at all. A real time system is divided into two systems: -

1.    Hard Real Time System.

2.    Soft Real Time System.

5.1 Hard Real Time System: -

                                            It guarantees the critical task be completed on time. This whole requires that all delays in the system be bounded. This type of system cannot be mixed with any another operating system. Since none of any general-purpose operating system is configure in this type of operating system.

5.2 Soft Real Time System: -

                                          This operating system is less restrictive than hard real time system. In this critical real time task gets a priority over other task. It can be mixed with other types of operating system. They are useful in multimedia, virtual reality and advance scientific method.

-: STRUCTURE OF OPERATING SYSTEM:-

(1) Monolithic System: -

                                    This operating system is written as a collection of procedures, each of which can call any other procedure whenever it needs. When this technique is used each procedure in the system has a well-defined interface in terms of parameters and results. In this system the information-hiding feature is not available. Every procedure is feasible to every another procedure. The system calls provided by the operating system are requested by putting the parameters in registers or on the stack and then executes a special trap instruction known as Kernel call or Supervisor call. The instruction switches the matching from user task to kernel mode (event 1). Most CPU has two modes : -

1.    Kernel mode : -

2.    User mode :-

1. Kernel : -

                 In this mode, the operating system in which all instructions are allowed.