Study Unit 4 computer systems and data communication



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Why Network Computers?


The primary purpose of a computer network is to share resources. Computers networks allow people to share information, software, and any resources, including hardware, more efficiently. For example:


  • You can play a CD music from one computer while sitting on another computer

  • You may have a computer with a CD writer or a backup system but the other computer doesn’t have it; In this case, you can burn CDs or make backups on a computer that has one of these but using data from a computer that doesn’t have a CD writer or a backup system

  • You may have a computer that doesn’t have a DVD player. In this case, you can place a movie DVD on the computer that has a DVD player, and then view the movie on a computer that lacks a DVD player

  • You can connect a printer (or a scanner, or a fax machine) to one computer and let other computers of the network print (or scan, or fax) to that printer (or scanner, or fax machine)

  • You can place a CD with pictures on one computer and let other computers access those pictures

  • You can create files and store them in one computer, then access those files from the other computer(s) connected to it











Components of a Network


In order to set up a computer network relevant network hardware and software are required.
Network hardware

Networking hardware includes all computers, peripherals, interface cards and other equipment needed to perform data-processing and communications within the network.

This section provides information on the following components:



  • File Servers

  • Workstations

  • Network Interface Cards

  • Switches

  • Repeaters

  • Bridges

  • Routers

File Server


A File server is a high capacity computer that provides various resources to the network. It is the heart of a network and must have the following things:

  • need network operating system such as Novell Netware, Windows NT server, or Apple Share

  • control the communication of information between the nodes on a network

If you plan to use one of your existing computers as the server, check its hardware and make sure it meets the following requirements:



  • A processor with 133-MHz or higher speed; 550-MHz recommended; up to eight processors supported on one server

  • 128 MB of RAM minimum required; 256 MB or more recommended; 32 GB maximum

  • 1.25 to 2 GB of available hard disk space

  • CD-ROM or DVD-ROM drive

  • VGA or hardware that supports console redirection required; Super VGA supporting 800 x 600 or higher-resolution monitor recommended

Workstations

A computer in a network is called a workstation or client. This computer needs a network interface card to enable it to be connected to the network backbone. It does not necessarily need floppy disk drives or hard disks since files can be saved on the file server.


When you are planning to use a computer as a workstation as a network, you should make sure that computer meets the necessary requirements. In some cases, it may only meet the hardware requirements without any software. In some cases, something could be missing. If you decide to purchase brand new computers, as a reminder of what we reviewed in chapter one, here are the hardware requirements the computer must meet:

  • A processor with 300 megahertz or higher processor clock speed recommended; 233 MHz minimum required (single or dual processor system); Intel Pentium/Celeron family, or AMD K6/Athlon/Duron family, or compatible processor recommended

  • 128 megabytes (MB) of RAM or higher recommended (64 MB minimum supported; may limit performance and some features)

  • 1.5 gigabytes (GB) of available hard disk space

  • Super VGA (800 x 600) or higher-resolution video adapter and monitor

  • CD-ROM or DVD drive

  • Keyboard

  • Microsoft Mouse or compatible pointing device


Network Interface Cards (NICs)

A network interface card (NIC) which is pronounced 'nick', is also known as a network card. It connects the computer to the cabling, which in turn links all of the computers on the network together. Each computer on a network must have a network card. The three common network interface connections are Ethernet cards, LocalTalk connectors, Token Ring cards. Most modern network cards are 10/100 NICs and can operate at either 10Mbps or 100Mbps Only NICs supporting a minimum of 100Mbps should be used in new installations schools. Most of these are internal, with the card fitting into an expansion slot inside the computer and some build on the motherboard.





Fig 5: Network Interface Cards (NICs)
We mentioned that a network card could also be used or installed externally. This can be done using USB. Here is another example:


Hubs/Concentrators

A hub is a device used to connect multiple devices, including PC, printers, and scanners, to the network. It serves as a central meeting place for cables from computers, servers and peripherals. To make this possible, a hub is equipped with small holes called ports. They usually have 4, 8, 12, or 24 RJ-45 ports. The entire network shuts down if there is a problem on a hub. Here are some examples of commonly found hubs.


Fig 6a: An 8 port Hub





Fig 6b: 2 Examples of 24 port Switches
When configuring a hub, you connect an RJ-45 cable from the network card of a computer to one port of the hub.
The function of a hub is to direct information around the network, facilitating communication between all connected devices. However in new installations switches should be used instead of hubs as they are more effective and provide better performance.



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