Study Unit 4 computer systems and data communication



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Study Unit

4

COMPUTER SYSTEMS AND DATA COMMUNICATION

Introduction


Computerised information systems use hardware and software to generate information. This information must then be communicated to the user by using specific communication methods. In this study unit, we look at information systems, accounting information systems and modern methods of communication.

Communication Theory

Communication is the transfer of information from a sender to a receiver. It refers to the means and methods whereby data is transferred between processing locations through the use of communication systems. Communication systems are defined as systems for creating, delivering and receiving electronic messages. The communication system comprises of the following

  • A device to send the message

  • The channel or communication media

  • A device to receive the message

An information system is a system that comprises people, machines and methods by which data is collected, processed, transferred and distributed. The system may be manual or automatic. This study unit will focus on the automatic system. An accounting information system measures business activities (data), processes the data and communicates usable information to decision makers.

What is a Network?

Before the evolution of networks, organisations made use of stand-alone computer systems. Computers would be found in strategic places in the organisation but were not linked to each other. Stand-alone computers are now used mainly by sole proprietors and for personal use.

Computer networks are now more accessible to organisations and individuals on a large scale. Terminals are linked to a mainframe and this gives users access to a central processing function. These terminals can be linked via internal or external communication channels.

A network consists of two or more computers that are linked in order to share resources, such as printers and CD-ROMs, exchange files, or allow electronic communications.

There are different configurations that can be used to ensure connectivity. Configuration refers to the way that hardware devices are connected to each other.

The computers on a network may be linked through cables, telephone lines, radio waves, satellites, or infrared light beams.


Fig 4.1 gives an example of a network in an organisation comprising a local area network or LAN connecting computers with each other, the Internet, and various servers.

The three basic types of networks include:



  • Local Area Network (LAN)

  • Wide Area Network (WAN)

  • Metropolitan Area Network (MAN)


Local Area Network

The Local Area Network (LAN) enables multiple users in a relatively small geographical area to exchange files and messages, as well as access shared resources such as file servers. Rarely are LAN computers more than a mile apart. It is generally limited to a geographic area such as a writing lab, school, or building.

In a typical LAN configuration, one computer is designated as the file server. It stores all of the software that controls the network, as well as the software that can be shared by the computers attached to the network. Computers connected to the file server are called workstations. The workstations can be less powerful than the file server, and they may have additional software on their hard drives. On most LANs, cables are used to connect the network interface cards in each computer.


Wide Area Network

The Wide Area Network (WAN) is an interconnection of various LANs through telephone network to unit geographically distributed users. Dedicated transoceanic cabling or satellite uplinks may be used to connect this type of network.
Using a WAN, anybody in Zimbabwe can communicate with countries like Japan in a matter of minutes, without paying enormous phone bills. For example when we log on to the Internet, we become a part of a WAN. A WAN uses special communication tools such as multiplexers to connect local and metropolitan networks to global communications networks like the Internet. To users, however, a WAN will not appear to be much different than a LAN or a MAN.
Metropolitan Area Network

The Metropolitan Area Network (MAN) is usually the interconnection between various LANs in a particular geographical area like a metropolitan city like Harare.



Computer Networks configurations

Basically, there are two types of network configuration, peer-to-peer networks and client/server networks.


A network is referred to as peer-to-peer if most computers are similar and run workstation operating systems. Peer-to-peer networks are more commonly implemented where less then ten computers are involved and where strict security is not necessary. All computers have the same status, hence the term 'peer', and they communicate with each other on an equal footing. Files, such as word processing or spreadsheet documents, can be shared across the network and all computers on the network can share devices, such as printers or scanners, which are connected to any one computer. Other computers can access these resources but a computer that has a particular resource must be turned on for other computers to access the resource it has. For example, if a printer is connected to computer A and computer B wants to print to that printer, computer A must be turned on.
A computer network is referred to as client/server if (at least) one of the computers is used to "serve" other computers referred to as "clients". Besides the computers, other types of devices can be part of the network. Client/server networks are more suitable for larger networks. A central computer, or 'server', acts as the storage location for files and applications shared on the network. Usually the server is a higher than average performance computer. The server also controls the network access of the other computers which are referred to as the 'client' computers. Typically, teachers and students in a school will use the client computers for their work and only the network administrator (usually a designated staff member) will have access rights to the server.
In a client/server environment, each computer still holds (or can still hold) its (or some) resources and files. Other computers can also access the resources stored in a computer, as in a peer-to-peer scenario. One of the particularities of a client/server network is that the files and resources are centralized. This means that a computer, the server, can hold them and other computers can access them. Since the server is always On, the client machines can access the files and resources without caring whether a certain computer is On.
Another big advantage of a client/server network is that security is created, managed, and can highly get enforced. To access the network, a person, called a user must provide some credentials, including a username and a password. If the credentials are not valid, the user can be prevented from accessing the network.

The client/server type of network also provides many other advantages such as centralized backup, Intranet capability, Internet monitoring, etc.


Table 4.1 provides a summary comparison between Peer-to-Peer and Client/Server Networks.

Table 1: Peer-to-Peer Networks vs Client/Server Networks

Peer-to-Peer Networks vs Client/Server Networks


Peer-to-Peer Networks

Client/Server Networks

Easy to set up

More difficult to set up

Less expensive to install

More expensive to install

Can be implemented on a wide range of operating systems

A variety of operating systems can be supported on the client computers, but the server needs to run an operating system that supports networking

More time consuming to maintain the software being used (as computers must be managed individually)

Less time consuming to maintain the software being used (as most of the maintenance is managed from the server)

Very low levels of security are supported or none at all. These can be very cumbersome to set up, depending on the operating system being used

High levels of security are supported, all of which are controlled from the server. Such measures prevent the deletion of essential system files or the changing of settings

Ideal for networks with less than 10 computers

No limit to the number of computers that can be supported by the network

Does not require a server

Requires a server running a server operating system

Demands a moderate level of skill to administer the network

Demands that the network administrator has a high level of IT skills with a good working knowledge of a server operating system


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