The various types of operating systems are as follows -
(i) Desktop system
(ii) Multiprocessor system
(iii) Clustered system
(iv) Handheld system
(v) Real-time system
(vi) Multitasking
(vii) Multiprogramming
(viii) Distributed system
(i) Desktop system :- Personal computers PCs introduced in the 1970s. During their first decade, the CPUs in PCs lacked the features needed to protect an operating system from use programs. Therefore, PC operating systems were neither multiuser nor multitasking. However, PC operating systems have changed with time; instead of maximizing CPU and peripheral utilization, the systems opt for maximizing user convenience and responsiveness. These systems include PCs running Microsoft Windows and the Apple Macintosh. The MS-DOS operating system from Microsoft has been superseded by multiple flavors of Microsoft Windows, and IBM has upgraded MS-DOS to the OS/2 multitasking system. The Apple Macintosh operating system has been ported to more advanced hardware, and now include new features, such as virtual memory and multitasking. Linux, a UNIX-like operating system available for PCs, has become popular recently.
(ii) Multiprocessor system :- Multiprocessing or multiprocessor operating manage the operation of computer systems that incorporate multiple processors. Multiprocessor operating systems are multitasking systems by defintion because they support simultaneous execution of multiple tasks on different processors. In other words, a computer system that contains two or more CPUs is called a multiprocessor system. It is also known as parallel systems or tightly coupled systems. These processors share the computer bus, the clock, memory and peripheral devices. For example, Univoc 100/94, Cyber ITO, IBM 3081 (9180), IBM 3084.
The most common multiprocessor systems use symmetric multiprocessing (SMP), in which each processor runs an identical copy of the operating system, and these copies communicate with one another as needed. some multiprocessor systems use asymmetric multiprocessing, in which each processor is assigned a specific task. A master processor controls the system; the other processors either look to the master for instruction or have predefined tasks. hence, this scheme defines a master-slave relationship.
(iii) Clustered system :- Clustered systems gather together multiple CPUs to accomplish computational work. however, clustered systems differ from parallel systems in that they are composed of two or more individual systems coupled together. The general definition of the term clustered computers share storage and are closely linked via LAN networking.
Clustering is usually performed to provide high availability. In asymmetric clustering, one machine is in hot standby mode while the other is running the applications. The hot standby host (machine) does nothing but monitor the active server. If that server fails, the hot standby host becomes the active server. In symmetric mode, two or more hosts are running applications, and they are monitoring each other.
Other forms of clusters include parallel and clusters and clustering over a WAN. Parallel clusters allow multiple hosts to access the same data on the shares storage.
(iv) Handheld system :- Handheld systems include personal digital assistants (PDAs), such as Palmpilots or cellular telephones with connectivity to a network such as the internet. Developers of handheld systems and applications face many challenges due to the limited size of such devices.
Many handheld systems have memory between 512kB and 8 MB. Hence, the operating system and applications must manage memory efficiently. This includes returning all allocated memory back to the memory manager once the memory is no longer being used.
Another issues of concern to developers of handheld devices is the speed of processor used in the device. Usually, processors for handheld devices run at a fraction of the speed of a processor in a PC. To achieve a faster processor in a handheld device requires a larger battery that would have to e replaced or recharged more frequently. but to minimize the size of handheld devices, smaller and slower processors are required which consume less power.
(v) Real-time system :- Real-time operating systems are used in environments where a large number of events, mostly external to the computer system, must be accepted and processed in a short time or within certain deadlines. Such applications are industrial control, telephone switching equipment, flight control, and real-time simulations.
The real-time operating systems can be of two types - hard real-time operating system and soft real-time operating system.
(i) Hard Real-time operating system:- These operating systems guarantee that critical tasks be completed within a certain range of time. For example, a robot is hired to weld a car body, if robot welds too early or too late, the car cannot be sold, so it is a hard real-time system that require to complete car welding by robot hardly on the time.
(ii) Soft Real-time operating system:- This operating system provides some relaxation in time limit. For example - Multimedia systems, digital audio system etc.
Explicit, programmer-defined and controlled processes are encountered in real-time systems. A separate process is charged with handling a single external event. The process is activated upon occurrence of the related even signaled by an interrupt. Multitasking operation is accomplished by scheduling processes for execution independently of each other. Each process is assigned a certain level of priority that corresponds to the relative importance of the event that it services. The processor is allocated to the highest-priority processes preempt execution of the lower-priority processes. This type of scheduling, called, priority-based preemptive scheduling is used by real-time systems.
(vi) Multitasking:- A multitasking operating system is distinguished by its ability to support concurrent execution of two or more active processes. Multitasking is usually implemented by maintaining code and data of several processes in memory simultaneously and by multiplexing processor and I/O devices among them. Multitasking is often coupled with hardware and software support for memory protection in order to prevent erroneous processes from corrupting address spaces and behaviour of other resident processes.
(vii) Multiprogramming :- The most important aspect of job scheduling is the ability to multiprogram. In general, a single user cannot keep either the CPU or the I/O devices busy at all times. Multiprogramming increases CPU utilization by organizing jobs so that the CPU always has one to execute.
The idea is to keep several jobs in memory simultaneously. This set of jobs is a subset of the jobs kept in the job pool - since the number of jobs that can be kept simultaneously in memory is usually much smaller than the number of jobs that can be in the job pool. The operating system picks and being to execute one of the jobs in the memory.
(viii) Distributed system:- In distributed system or loosely coupled system processors do not share memory, and each processor has its own local memory. Therefore, a processor cannot directly access the memory attached to other processors. Loosely coupled systems use only message passing for interprocessor communication and synchronization. In loosely coupled systems, the processor of distributed computing system can be located far from each other to cover a wider geographical area. In these systems, the intermachine message delay in large and the data rate is low. An example of loosely coupled system is intel's hypercube.
Comments
Post a Comment