TYPES OF SYSTEM (page-3)

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 2. DESKTOP SYSTEMS

A desktop system is a personal computer (PC) system in a form intended for regular use at a single location, as opposed to a mobile ,laptop or portable computer.Early desktop computers were designed to lay flat on the desk, while modern towers stand upright. Most modern desktop computer systems have separate screens and keyboards. Modern ones all support multiprogramming, often with dozens of programs started up at boot time. Their job is to provide good support to a single user. They are widely used for word processing, spreadsheets, and Internet access. Common examples are Linux, FreeBSD, Windows 8, and the Macintosh operating system.

3. MULTIPROCESSOR SYSTEMS

1.Multiprocessing is the use of two or more central processing units (CPUs) within a single computer system. The term also refers to the ability of a system to support more than one processor and/or the ability to allocate tasks between them.33] There are many variations on this basic theme, and the definition of multiprocessing can vary with context, mostly as a function of how CPUs are defined (multiple cores on one die, multiple dies in one package, multiple packages in one system unit, etc.). .A multiprocessor is a computer system having two or more processing units (multiple processors) each sharing main memory and peripherals, in order to simultaneously process programs 4.multiprocessing is divided into symmetric multiprocessing (SMP) and massively parallel processing 5.In symmetric (or "tightly coupled") multiprocessing, the processors share memory and the I/O bus or data path. A single copy of the operating system is in charge of all the processors. SMP, also known as a "shared everything" system, does not usually exceed 16 processors. 6.In massively parallel (or "loosely coupled") processing, up to 200 or more processors can work on the same application. Each processor has its own operating system and memory, but an "interconnect" arrangement of data paths allows messages to be sent between processors

ADVANTAGES OF MULTIPROCESSOR SYSTEMS

1.     Increased throughput - Faster execution, but not 100% linear speedup.
2.     Economy of scale - Peripherals, disks, memory, shared among processors.
3.     Increased reliability
1.         Failure of a CPU slows system, doesn't crash it.
2.         Redundant processing provides system of checks and balances. ( e.g. NASA )

 

4. Distributed operating System

Distributed systems use multiple central processors to serve multiple real time application and multiple users.

Data processing jobs are distributed among the processors accordingly to which one can perform each job most efficiently.

The processors communicate with one another through various communication lines (such as high-speed buses or telephone lines).

These are referred as loosely coupled systems or distributed systems. Processors in a distributed system may vary in size and function.

These processors are referred as sites, nodes, computers and so on.

The advantages of distributed systems are following.

1.     With resource sharing facility user at one site may be able to use the resources available at another.
2.     Speedup the exchange of data with one another via electronic mail.
3.     If one site fails in a distributed system, the remaining sites can potentially continue operating.
4.     Better service to the customers.
5.     Reduction of the load on the host computer.
6.     Reduction of delays in data processing.

 

 5. CLUSTERED SYSTEMS

A computer cluster consists of a set of loosely connected computers that work together so that in many respects they can be viewed as a single system. The components of a cluster are usually connected to each other through fast local area networks , each node (computer used as a server) running its own instance of an operating system . Computer clusters emerged as a result of convergence of a number of computing trends including the availability of low cost microprocessors, high speed networks, and software for high performance distributed computing . In Clustered systems, if the monitored machine fails, the monitoring machine can take ownership of its storage, and restart the application(s) that were running on the failed machine. The failed machine can remain down, but the users and clients of the application would only see a brief interruption of the service. 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. It does require that more than one application be available to run. Other forms of clusters include parallel clusters and clustering over a WAN. Parallel clusters allow multiple hosts to access the same data on the shared storage and are usually accomplished by special version of software and special releases of applications. For example, Oracle Parallel Server is a version of Oracle’s data base that has been designed to run parallel clusters. Storage - area networks (SANs) are the feature development of the clustered systems includes the multiple hosts to multiple storage units

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