Distribution


 * Distributed computing** is a method of computer processing in which different parts of a program are run simultaneously on two or more computers that are communicating with each other over a network. Distributed computing is a type of **segmented** or [|parallel computing], but the latter term is most commonly used to refer to processing in which different parts of a program run simultaneously on two or more processors that are part of the same computer. While both types of processing require that a program be segmented—divided into sections that can run simultaneously, distributed computing also requires that the division of the program take into account the different environments on which the different sections of the program will be running. For example, two computers are likely to have different file systems and different hardware components.

=**What is Distributed Computing?**= A distributed computer system consists of multiple software components that are on multiple computers, but run as a single system. The computers that are in a distributed system can be physically close together and connected by a local network, or they can be geographically distant and connected by a wide area network. A distributed system can consist of any number of possible configurations, such as mainframes, personal computers, workstations, minicomputers, and so on. The goal of distributed computing is to make such a network work as a single computer. Distributed systems offer many benefits over centralized systems, including the following:


 * Scalability** The system can easily be expanded by adding more machines as needed.

Distributed computing systems can run on hardware that is provided by many vendors, and can use a variety of standards-based software components. Such systems are independent of the underlying software. They can run on various operating systems, and can use various communications protocols. Some hardware might use UNIX(R) as the operating system, while other hardware might use Windows operating systems. For intermachine communications, this hardware can use SNA or TCP/IP on Ethernet or Token Ring.
 * Redundancy** Several machines can provide the same services, so if one is unavailable, work does not stop. Additionally, because many smaller machines can be used, this redundancy does not need to be prohibitively expensive.
 * the image above shows an example of such a distributed system. This system contains two local area networks (LANs) that are connected to each other. One LAN consists of UNIX workstations from several different manufacturers; the other LAN consists primarily of PCs that are running several different PC operating systems. One of the LANs is also connected to a mainframe by way of an SNA connection.

Three - tiered client/ server architecture
A common design of client/server systems uses three tiers:
 * 1) A client that interacts with the user
 * 2) An application server that contains the business logic of the application
 * 3) A resource manager that stores data



Resources: what is distributed computing. (2002, March 5). //TX series for multiplatform. IBM.// [|http://publib.boulder.ibm.com/infocenter/txformp/v6r0m0/index.jsp?topic=/com.ibm.cics.te.doc/erziaz0015.htm]

last edited on Jan 21 by janicema